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Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK color ...
on the spectrum of visible light. The eye perceives blue when observing light with a dominant wavelength between approximately 450 and 495
nanometre 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
s. Most blues contain a slight mixture of other colours;
azure Azure may refer to: Colour * Azure (color), a hue of blue ** Azure (heraldry) ** Shades of azure, shades and variations Arts and media * ''Azure'' (Art Farmer and Fritz Pauer album), 1987 * Azure (Gary Peacock and Marilyn Crispell album), 2013 ...
contains some green, while ultramarine contains some violet. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called Tyndall effect explains blue eyes. Distant objects appear more blue because of another optical effect called
aerial perspective Aerial perspective, or atmospheric perspective, refers to the effect the atmosphere has on the appearance of an object as viewed from a distance. As the distance between an object and a viewer increases, the contrast between the object and its b ...
. Blue has been an important colour in art and decoration since ancient times. The semi-precious stone
lapis lazuli Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines, ...
was used in ancient Egypt for jewellery and ornament and later, in the Renaissance, to make the pigment ultramarine, the most expensive of all pigments. In the eighth century Chinese artists used
cobalt blue Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter ...
to colour fine
blue and white porcelain "Blue and white pottery" () covers a wide range of white pottery and porcelain decorated under the glaze with a blue pigment, generally cobalt oxide. The decoration is commonly applied by hand, originally by brush painting, but nowadays by sten ...
. In the Middle Ages, European artists used it in the windows of cathedrals. Europeans wore clothing coloured with the vegetable dye woad until it was replaced by the finer indigo from America. In the 19th century, synthetic blue dyes and pigments gradually replaced organic dyes and mineral pigments. Dark blue became a common colour for military uniforms and later, in the late 20th century, for business suits. Because blue has commonly been associated with harmony, it was chosen as the colour of the flags of the United Nations and the European Union. Surveys in the US and Europe show that blue is the colour most commonly associated with harmony, faithfulness, confidence, distance, infinity, the imagination, cold, and occasionally with sadness. In US and European public opinion polls it is the most popular colour, chosen by almost half of both men and women as their favourite colour. The same surveys also showed that blue was the colour most associated with the masculine, just ahead of black, and was also the colour most associated with intelligence, knowledge, calm, and concentration.


Etymology and linguistics

The modern English word ''blue'' comes from Middle English or , from the Old French , a word of Germanic origin, related to the Old High German word (meaning 'shimmering, lustrous').''Webster's Seventh New Collegiate Dictionary'' (1970). In
heraldry Heraldry is a discipline relating to the design, display and study of armorial bearings (known as armory), as well as related disciplines, such as vexillology, together with the study of ceremony, rank and pedigree. Armory, the best-known branch ...
, the word ''
azure Azure may refer to: Colour * Azure (color), a hue of blue ** Azure (heraldry) ** Shades of azure, shades and variations Arts and media * ''Azure'' (Art Farmer and Fritz Pauer album), 1987 * Azure (Gary Peacock and Marilyn Crispell album), 2013 ...
'' is used for ''blue''. In Russian, Spanish and some other languages, there is no single word for blue, but rather different words for light blue (, ; ) and dark blue (, ; ). See
Colour term A color term (or color name) is a word or phrase that refers to a specific color. The color term may refer to human perception of that color (which is affected by visual context) which is usually defined according to the Munsell color system, or ...
. Several languages, including Japanese and Lakota Sioux, use the same word to describe blue and green. For example, in Vietnamese, the colour of both tree leaves and the sky is . In Japanese, the word for blue (, ) is often used for colours that English speakers would refer to as green, such as the colour of a traffic signal meaning "go". In Lakota, the word is used for both blue and green, the two colours not being distinguished in older Lakota. (For more on this subject, see Distinguishing blue from green in language.) Linguistic research indicates that languages do not begin by having a word for the colour blue. Colour names often developed individually in natural languages, typically beginning with black and white (or dark and light), and then adding red, and only much later – usually as the last main category of colour accepted in a language – adding the colour blue, probably when blue pigments could be manufactured reliably in the culture using that language.


Optics and colour theory

Human eyes perceive blue when observing light which has a dominant wavelength of roughly 450–495 nanometres. Blues with a higher frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency and a longer wavelength gradually appear more green. Pure blue, in the middle, has a wavelength of 470 nanometres. Isaac Newton included blue as one of the seven colours in his first description the visible spectrum. He chose seven colours because that was the number of notes in the musical scale, which he believed was related to the optical spectrum. He included indigo, the hue between blue and violet, as one of the separate colours, though today it is usually considered a hue of blue. In painting and traditional colour theory, blue is one of the three primary colours of pigments (red, yellow, blue), which can be mixed to form a wide gamut of colours. Red and blue mixed together form violet, blue and yellow together form green. Mixing all three primary colours together produces a dark brown. From the Renaissance onward, painters used this system to create their colours. (See RYB colour model.) The RYB model was used for colour printing by Jacob Christoph Le Blon as early as 1725. Later, printers discovered that more accurate colours could be created by using combinations of cyan, magenta, yellow, and black ink, put onto separate inked plates and then overlaid one at a time onto paper. This method could produce almost all the colours in the spectrum with reasonable accuracy. File:AdditiveColorMixing.svg, Additive colour mixing. The combination of primary colours produces secondary colours where two overlap; the combination red, green, and blue each in full intensity makes white. File:Closeup of pixels.JPG, Red, green, and blue
subpixels In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...
on an
LCD display A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but in ...
.
On the HSV colour wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel based on traditional colour theory ( RYB) where blue was considered a primary colour, its complementary colour is considered to be orange (based on the Munsell colour wheel). Lasers emitting in the blue region of the spectrum became widely available to the public in 2010 with the release of inexpensive high-powered 445–447 nm laser diode technology. Previously the blue wavelengths were accessible only through DPSS which are comparatively expensive and inefficient, but still widely used by scientists for applications including optogenetics,
Raman spectroscopy Raman spectroscopy () (named after Indian physicist C. V. Raman) is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman sp ...
, and particle image velocimetry, due to their superior beam quality. Blue gas lasers are also still commonly used for holography,
DNA sequencing DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...
,
optical pumping Optical pumping is a process in which light is used to raise (or "pump") electrons from a lower energy level in an atom or molecule to a higher one. It is commonly used in laser construction to pump the active laser medium so as to achieve populat ...
, among other scientific and medical applications.


Shades and variations

Blue is the colour of light between violet and
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK color ...
on the visible spectrum. Hues of blue include indigo and ultramarine, closer to violet; pure blue, without any mixture of other colours; Azure, which is a lighter shade of blue, similar to the colour of the sky; Cyan, which is midway in the spectrum between blue and green, and the other blue-greens such as turquoise, teal, and aquamarine. Blue also varies in shade or tint; darker shades of blue contain black or grey, while lighter tints contain white. Darker shades of blue include ultramarine,
cobalt blue Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter ...
, navy blue, and
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
; while lighter tints include sky blue,
azure Azure may refer to: Colour * Azure (color), a hue of blue ** Azure (heraldry) ** Shades of azure, shades and variations Arts and media * ''Azure'' (Art Farmer and Fritz Pauer album), 1987 * Azure (Gary Peacock and Marilyn Crispell album), 2013 ...
, and Egyptian blue. (For a more complete list see the List of colours).


As a structural colour

In nature, many blue phenomena arise from structural colouration, the result of interference between reflections from two or more surfaces of thin films, combined with refraction as light enters and exits such films. The geometry then determines that at certain angles, the light reflected from both surfaces interferes constructively, while at other angles, the light interferes destructively. Diverse colours therefore appear despite the absence of colourants.


Colourants

File:Egyptian blue.jpg, Egyptian blue File:Cobalt Blue.JPG,
Cobalt blue Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter ...
. File:Bleu phtalo.jpg, Copper phthalocyanine. File:YInMn_Blue_-_cropped.jpg, YInMn blue. File:Prussian blue.jpg,
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
, Fe CN)">Cyanide.html" ;"title="e(Cyanide">CN) is the blue of blueprint">Cyanide">CN<_a>).html" ;"title="Cyanide.html" ;"title="e(Cyanide">CN)">Cyanide.html" ;"title="e(Cyanide">CN) is the blue of blueprints.


Artificial blues

Egyptian blue, the first artificial pigment, was produced in the third millennium BC in Ancient Egypt. It is produced by heating pulverized sand, copper, and natron. It was used in tomb paintings and funereal objects to protect the dead in their afterlife. Prior to the 1700s, blue colourants for artwork were mainly based on lapis lazuli and the related mineral ultramarine. A breakthrough occurred in 1709 when German druggist and pigment maker
Johann Jacob Diesbach Johann Jacob Diesbach () (born around 1670 – died in 1748), also written as Johann Jacob von Diesbach, was a Swiss pigment and dye producer known for first synthesizing a blue pigment known as Prussian blue (i.e. iron blue or Berlin blue). Bio ...
discovered
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
. The new blue arose from experiments involving heating dried blood with iron sulphides and was initially called Berliner Blau. By 1710 it was being used by the French painter Antoine Watteau, and later his successor Nicolas Lancret. It became immensely popular for the manufacture of wallpaper, and in the 19th century was widely used by French impressionist painters. Beginning in the 1820s, Prussian blue was imported into Japan through the port of Nagasaki. It was called ''bero-ai'', or Berlin blue, and it became popular because it did not fade like traditional Japanese blue pigment, ''ai-gami'', made from the dayflower. Prussian blue was used by both
Hokusai , known simply as Hokusai, was a Japanese ukiyo-e artist of the Edo period, active as a painter and printmaker. He is best known for the woodblock printing in Japan, woodblock print series ''Thirty-Six Views of Mount Fuji'', which includes the ...
, in his wave paintings, and Hiroshige. In 1799 a French chemist,
Louis Jacques Thénard Louis Jacques Thénard (4 May 177721 June 1857) was a French chemist. Life He was born in a farm cottage near Nogent-sur-Seine in the Champagne district the son of a farm worker. In the post-Revolution French educational system , most boys rec ...
, made a synthetic cobalt blue pigment which became immensely popular with painters. In 1824 the Societé pour l'Encouragement d'Industrie in France offered a prize for the invention of an artificial ultramarine which could rival the natural colour made from lapis lazuli. The prize was won in 1826 by a chemist named Jean Baptiste Guimet, but he refused to reveal the formula of his colour. In 1828, another scientist, Christian Gmelin then a professor of chemistry in Tübingen, found the process and published his formula. This was the beginning of new industry to manufacture artificial ultramarine, which eventually almost completely replaced the natural product. In 1878 German chemists synthesized indigo. This product rapidly replaced natural indigo, wiping out vast farms growing indigo. It is now the blue of blue jeans. As the pace of organic chemistry accelerated, a succession of synthetic blue dyes were discovered including Indanthrone blue, which had even greater resistance to fading during washing or in the sun, and copper phthalocyanine. File:The Blue Boy.jpg, The Blue Boy (1770), featuring lapis lazuli, indigo, and cobalt colourants, File:Great Wave off Kanagawa2.jpg, The Great Wave off Kanagawa illustrates the use of
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
File:Indigoproduktion BASF 1890.JPG, A synthetic indigo dye factory in Germany in 1890.


Dyes for textiles and food

Blue dyes are organic compounds, both synthetic and natural. Woad and true indigo were once used but since the early 1900s, all indigo is synthetic. Produced on an industrial scale, indigo is the blue of blue jeans. For food, the triarylmethane dye Brilliant blue FCF is used for candies. The search continues for stable, natural blue dyes suitable for the food industry.


Pigments for painting and glass

Blue pigments were once produced from minerals, especially
lapis lazuli Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines, ...
and its close relative ultramarine. These minerals were crushed, ground into powder, and then mixed with a quick-drying binding agent, such as egg yolk ( tempera painting); or with a slow-drying oil, such as
linseed oil Linseed oil, also known as flaxseed oil or flax oil (in its edible form), is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant (''Linum usitatissimum''). The oil is obtained by pressing, sometimes followed by ...
, for oil painting. Two inorganic but synthetic blue pigments are
cerulean blue Cerulean (), also spelled caerulean, is a shade of blue ranging between azure and a darker sky blue. The first recorded use of ''cerulean'' as a colour name in English was in 1590. The word is derived from the Latin word '' caeruleus'', "da ...
(primarily cobalt(II) stanate: ) and
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
(milori blue: primarily ). The chromophore in blue glass and glazes is cobalt(II). Diverse cobalt(II) salts such as cobalt carbonate or cobalt(II) aluminate are mixed with the silica prior to firing. The cobalt occupies sites otherwise filled with silicon.


Inks

Methyl blue Methyl blue is a chemical compound with the molecular formula C37H27N3Na2O9S3. It is used as a stain in histology, and stains collagen blue in tissue sections. It can be used in some differential staining techniques such as Mallory's connec ...
is the dominant blue pigment in inks used in pens. Blueprinting involves the production of
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
in situ.


Inorganic compounds

Certain metal ions characteristically form blue solutions or blue salts. Of some practical importance, cobalt is used to make the deep blue glazes and glasses. It substitutes for silicon or aluminum ions in these materials. Cobalt is the blue
chromophore A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...
in
stained glass windows Stained glass is coloured glass as a material or works created from it. Throughout its thousand-year history, the term has been applied almost exclusively to the windows of churches and other significant religious buildings. Although tradition ...
, such as those in Gothic cathedrals and in Chinese porcelain beginning in the T'ang Dynasty. Copper(II) (Cu2+) also produces many blue compounds, including the commercial algicide copper(II) sulfate (CuSO4.5H2O). Similarly, vanadyl salts and solutions are often blue, e.g.
vanadyl sulfate Vanadyl(IV) sulfate describes a collection of inorganic compounds of vanadium with the formula, VOSO4(H2O)x where 0 ≤ x ≤ 6. The pentahydrate is common. This hygroscopic blue solid is one of the most common sources of vanadium in the laborator ...
.


In nature


Sky and sea

When sunlight passes through the atmosphere, the blue wavelengths are scattered more widely by the oxygen and nitrogen molecules, and more blue comes to our eyes. This effect is called Rayleigh scattering, after Lord Rayleigh and confirmed by Albert Einstein in 1911. The sea is seen as blue for largely the same reason: the water absorbs the longer wavelengths of red and reflects and scatters the blue, which comes to the eye of the viewer. The deeper the observer goes, the darker the blue becomes. In the open sea, only about one per cent of light penetrates to a depth of 200 metres. (See underwater and
euphotic depth The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological pr ...
) The colour of the sea is also affected by the colour of the sky, reflected by particles in the water; and by
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
and plant life in the water, which can make it look green; or by sediment, which can make it look brown. The farther away an object is, the more blue it often appears to the eye. For example, mountains in the distance often appear blue. This is the effect of atmospheric perspective; the farther an object is away from the viewer, the less contrast there is between the object and its background colour, which is usually blue. In a painting where different parts of the composition are blue, green and red, the blue will appear to be more distant, and the red closer to the viewer. The cooler a colour is, the more distant it seems. Blue light is scattered more than other wavelengths by the gases in the
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, hence our "blue planet". File:Top of Atmosphere.jpg, Earth's blue halo when seen from space. File:Aerial perspective 1.JPG, Another example of Rayleigh scattering. File:LightningVolt Deep Blue Sea.jpg, The sea.


Minerals

Lapis-lazuli hg.jpg, Lapis-lazuli Azurite from China.jpg, Azurite Natural ultramarine pigment.jpg, Natural ultramarine pigment Logan Sapphire SI.jpg, Logan sapphire Some of the most desirable gems are blue, including sapphire and tanzanite. Compounds of copper(II) are characteristically blue and so are many copper-containing minerals. Azurite (, with a deep blue colour, was once employed in medieval years, but it is unstable pigment, losing its colour especially under dry conditions.
Lapis lazuli Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines, ...
, mined in Afghanistan for more than three thousand years, was used for jewelry and ornaments, and later was crushed and powdered and used as a pigment. The more it was ground, the lighter the blue colour became. Natural ultramarine, made was the finest available blue pigment in the Middle Ages and the Renaissance. It was extremely expensive, and in Italian Renaissance art, it was often reserved for the robes of the Virgin Mary.


Plants and fungi

File:Blaue Primeln.JPG, ''Primula acaulis'' File:Ipomoea August 2007-1.jpg, Morning glory (''
Ipomoea acuminata ''Ipomoea indica'' is a species of flowering plant in the family Convolvulaceae, known by several common names, including blue morning glory, oceanblue morning glory, ''koali awa'', and blue dawn flower. It bears heart-shaped or 3-lobed leaves an ...
'') File:Vaccinium corymbosum Beeren.jpg, '' Vaccinium corymbosum'' File:Delphinium denudatum 1.jpg, Blue Delphinium flower File:Lactarius indigo 48568 edit.jpg, '' Lactarius indigo''
Intense efforts have focused on blue flowers and the possibility that natural blue colourants could be used as food dyes. Commonly, blue colours in plants are
anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
s: "the largest group of water-soluble pigments found widespread in the plant kingdom." In the few plants that exploit structural colouration, brilliant colours are produced by structures within cells. The most brilliant blue colouration known in any living tissue is found in the marble berries of '' Pollia condensata'', where a spiral structure of cellulose fibrils scattering blue light. The fruit of quandong (Santalum acuminatum) can appear blue owing to the same effect.


Animals

File:Morpho didius Male Dos MHNT.jpg, Morpho butterfly File:Indigo Bunting by Dan Pancamo 4.jpg, Indigo buntings have iridescent feathers. File:Mandrill-k-means.png, Blue facial ridges of
mandrill The mandrill (''Mandrillus sphinx'') is a large Old World monkey native to west central Africa. It is one of the most colorful mammals in the world, with red and blue skin on its face and posterior. The species is sexually dimorphic, as males ...
File:2009-03-29Dendrobates tinctorius azureus106.jpg, Blue poison dart frog File:Synchiropus splendidus 2 Luc Viatour cropped.png, The mandarin fish is one of few animal species with blue pigment File:RanaArvalisBlueMale3.jpg, Male moor frogs become blue during the height of mating season
Blue-pigmented animals are relatively rare. Examples of which include butterflies of the genus '' Nessaea'', where blue is created by pterobilin. Other blue pigments of animal origin include phorcabilin, used by other butterflies in '' Graphium'' and '' Papilio'' (specifically '' P. phorcas'' and '' P. weiskei''), and sarpedobilin, which is used by ''
Graphium sarpedon ''Graphium sarpedon'', the common bluebottle or blue triangle in Australia, is a species of swallowtail butterfly that is found in South and Southeast Asia, as well as eastern Australia. There are approximately sixteen subspecies with differi ...
''. Blue-pigmented organelles, known as "cyanosomes", exist in the chromatophores of at least two fish species, the mandarin fish and the picturesque dragonet. More commonly, blueness in animals is a structural colouration; an optical interference effect induced by organized nanometer-sized scales or fibres. Examples include the plumage of several birds like the
blue jay The blue jay (''Cyanocitta cristata'') is a passerine bird in the family Corvidae, native to eastern North America. It lives in most of the eastern and central United States; some eastern populations may be migratory. Resident populations are a ...
and indigo bunting, the scales of butterflies like the morpho butterfly,
collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
fibres in the skin of some species of monkey and
opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered North ...
, and the
iridophore Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast, ...
cells in some fish and frogs.


Eyes

Blue eyes do not actually contain any blue pigment. Eye colour is determined by two factors: the pigmentation of the eye's iris and the
scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...
of light by the turbid medium in the stroma of the iris. In humans, the pigmentation of the iris varies from light brown to black. The appearance of blue, green, and hazel eyes results from the Tyndall scattering of light in the stroma, an optical effect similar to what accounts for the blueness of the sky. The irises of the eyes of people with blue eyes contain less dark melanin than those of people with brown eyes, which means that they absorb less short-wavelength blue light, which is instead reflected out to the viewer. Eye colour also varies depending on the lighting conditions, especially for lighter-coloured eyes. Blue eyes are most common in Ireland, the Baltic Sea area and Northern Europe, and are also found in Eastern,
Central Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known as ...
, and Southern Europe. Blue eyes are also found in parts of Western Asia, most notably in Afghanistan, Syria, Iraq, and Iran. In Estonia, 99% of people have blue eyes. In Denmark in 1978, only 8% of the population had brown eyes, though through immigration, today that number is about 11%. In Germany, about 75% have blue eyes. In the United States, as of 2006, one out of every six people, or 16.6% of the total population, and 22.3% of the white population, have blue eyes, compared with about half of Americans born in 1900, and a third of Americans born in 1950. Blue eyes are becoming less common among American children. In the US, boys are 3–5 per cent more likely to have blue eyes than girls.


History


In the ancient world

File:Lapis bowl Iran.JPG,
Lapis lazuli Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines, ...
bowl from Iran, end of 3rd – beginning of 2nd millennium BC (Louvre Museum) File:Tripodic goblet Louvre AO4079.jpg, Egyptian blue tripodic beaker imitating lapis lazuli. South Mesopotamia. (1399-1200 BC) File:WLA metmuseum Wall painting Polyphemus and Galaltea 4.jpg, Fresco of Polyphemus and Galatea, Pompei, using Egyptian blue (1st c. BC) (Metropolitan Museum)
As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines,David Bomford and Ashok Roy, ''A Closer Look- Colour'' (2009), National Gallery Company, London, () in Shortugai, and in other mines in Badakhshan province in northeast Afghanistan. Lapis lazuli artifacts, dated to 7570 BC, have been found at Bhirrana, which is the oldest site of Indus Valley civilisation. Lapis was highly valued by the Indus Valley Civilisation (7570–1900 BC). Lapis beads have been found at Neolithic burials in Mehrgarh, the Caucasus, and as far away as
Mauritania Mauritania (; ar, موريتانيا, ', french: Mauritanie; Berber: ''Agawej'' or ''Cengit''; Pulaar: ''Moritani''; Wolof: ''Gànnaar''; Soninke:), officially the Islamic Republic of Mauritania ( ar, الجمهورية الإسلامية ...
. It was used in the funeral mask of Tutankhamun (1341–1323 BC). A term for Blue was relatively rare in many forms of ancient art and decoration, and even in ancient literature. The Ancient Greek poets described the sea as green, brown or "the colour of wine". The colour was not mentioned in the Hebrew Bible. Reds, blacks, browns, and ochres are found in
cave painting In archaeology, Cave paintings are a type of parietal art (which category also includes petroglyphs, or engravings), found on the wall or ceilings of caves. The term usually implies prehistoric origin, and the oldest known are more than 40,000 ye ...
s from the Upper
Paleolithic The Paleolithic or Palaeolithic (), also called the Old Stone Age (from Greek: παλαιός ''palaios'', "old" and λίθος ''lithos'', "stone"), is a period in human prehistory that is distinguished by the original development of stone too ...
period, but not blue. Blue was also not used for dyeing fabric until long after red, ochre, pink, and purple. This is probably due to the perennial difficulty of making blue dyes and pigments. On the other hand, the rarity of blue pigment made it even more valuable. The earliest known blue dyes were made from plants – woad in Europe, indigo in Asia and Africa, while blue pigments were made from minerals, usually either
lapis lazuli Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines, ...
or azurite, and required more. Blue glazes posed still another challenge since the early blue dyes and pigments were not thermally robust. In ca. 2500 BC, the blue glaze Egyptian blue was introduced for ceramics, as well as many other objects.Chase, W.T. 1971, "Egyptian blue as a pigment and ceramic material." In: R. Brill (ed.) ''Science and Archaeology''. Cambridge, Mass: MIT Press. The Greeks imported indigo dye from India, calling it indikon, and they painted with Egyptian blue. Blue was not one of the four primary colours for Greek painting described by Pliny the Elder (red, yellow, black, and white). For the Romans, blue was the colour of mourning, as well as the colour of barbarians. The Celts and Germans reportedly dyed their faces blue to frighten their enemies, and tinted their hair blue when they grew old. The Romans made extensive use of indigo and Egyptian blue pigment, as evidenced, in part, by frescos in
Pompeii Pompeii (, ) was an ancient city located in what is now the ''comune'' of Pompei near Naples in the Campania region of Italy. Pompeii, along with Herculaneum and many villas in the surrounding area (e.g. at Boscoreale, Stabiae), was buried ...
. The Romans had many words for varieties of blue, including , , , , , , , and , but two words, both of foreign origin, became the most enduring; , from the Germanic word ''blau'', which eventually became ''bleu'' or blue; and , from the Arabic word , which became azure. Blue was widely used in the decoration of churches in the Byzantine Empire. By contrast, in the Islamic world, blue was of secondary to green, believed to be the favourite colour of the Prophet Mohammed. At certain times in Moorish Spain and other parts of the Islamic world, blue was the colour worn by Christians and Jews, because only Muslims were allowed to wear white and green.


In the Middle Ages

File:Vitraux Saint-Denis 190110 19.jpg, Stained glass window at Saint Denis Basilica (1130-1140), coloured with
cobalt blue Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter ...
File:Vitrail Chartres Notre-Dame 210209 1.jpg, Detail of the Blue Virgin Window, Chartres Cathedral (12th c.) File:Wilton diptych.jpg, The Wilton Diptych (1395–1399). The Virgin Mary was traditionally shown in blue(14th c.)
In the art and life of Europe during the early Middle Ages, blue played a minor role. This changed dramatically between 1130 and 1140 in Paris, when the Abbe Suger rebuilt the Saint Denis Basilica. Suger considered that light was the visible manifestation of the Holy Spirit. He installed
stained glass Stained glass is coloured glass as a material or works created from it. Throughout its thousand-year history, the term has been applied almost exclusively to the windows of churches and other significant religious buildings. Although tradition ...
windows coloured with cobalt, which, combined with the light from the red glass, filled the church with a bluish violet light. The church became the marvel of the Christian world, and the colour became known as the . In the years that followed even more elegant blue stained glass windows were installed in other churches, including at Chartres Cathedral and Sainte-Chapelle in Paris. In the 12th century the Roman Catholic Church dictated that painters in Italy (and the rest of Europe consequently) to paint the Virgin Mary with blue, which became associated with holiness, humility and virtue. In medieval paintings, blue was used to attract the attention of the viewer to the Virgin Mary. Paintings of the mythical
King Arthur King Arthur ( cy, Brenin Arthur, kw, Arthur Gernow, br, Roue Arzhur) is a legendary king of Britain, and a central figure in the medieval literary tradition known as the Matter of Britain. In the earliest traditions, Arthur appears as a ...
began to show him dressed in blue. The coat of arms of the kings of France became an azure or light blue shield, sprinkled with golden fleur-de-lis or lilies. Blue had come from obscurity to become the royal colour.


Renaissance through 18th century

Blue came into wider use beginning in the Renaissance, when artists began to paint the world with perspective, depth, shadows, and light from a single source. In Renaissance paintings, artists tried to create harmonies between blue and red, lightening the blue with lead white paint and adding shadows and highlights. Raphael was a master of this technique, carefully balancing the reds and the blues so no one colour dominated the picture. Ultramarine was the most prestigious blue of the Renaissance, being more expensive than gold. Wealthy art patrons commissioned works with the most expensive blues possible. In 1616 Richard Sackville commissioned a portrait of himself by Isaac Oliver with three different blues, including ultramarine pigment for his stockings. File:Oliver Richard Sackville Earl of Dorset 1616.jpg, Portrait of Richard Sackville (1616), using three expensive blues, including ultramarine for his stockings File:MET DP251168.jpg, Ming Dynasty, Porcelain vase painted with cobalt blue under transparent glaze. (15th c.) (Metropolitan Museum) File:Delftware plaque with New Testament scene 002.jpg, Delftware plaque with cobalt blue painting (1683) (Rijksmuseum, Amsterdam) File:Urn with cover MET DP104608.jpg, Urn by Josiah Wedgewood (1780s) (Metropolitan Museum) File:Johannes Vermeer - Girl with a Pearl Earring - WGA24666.jpg, "Girl with a Pearl Earring" by Johannes Vermeer features ultramarine pigment An industry for the manufacture of fine blue and white pottery began in the 14th century in Jingdezhen, China, using white Chinese porcelain decorated with patterns of
cobalt blue Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter ...
, imported from Persia. It was first made for the family of the Emperor of China, then was exported around the world, with designs for export adapted to European subjects and tastes. The Chinese blue style was also adapted by Dutch craftsmen in elft and English craftsmen in Staffordshire in the 17th-18th centuries. in the 18th century, blue and white porcelains were produced by Josiah Wedgwood and other British craftsmen.


19th-20th century

File:BrummellDighton1805.jpg,
Beau Brummel George Bryan "Beau" Brummell (7 June 1778 – 30 March 1840) was an important figure in Regency England and, for many years, the arbiter of men's fashion. At one time, he was a close friend of the Prince Regent, the future King George IV, but ...
(1776-1840) introduced the ancestor of the modern blue suit File:A Miner in His Cabin.jpg, A California gold miner in blue jeans (1853) File:Ferdinand Krumholz Isabel do Brasil 1853.jpg, Isabel, Princess Imperial of Brazil in blue gown (1853) File:New York Metropolitan Police Uniforms 1871.jpg, New York City police in 1871
The early 19th century saw the ancestor of the modern blue business suit, created by
Beau Brummel George Bryan "Beau" Brummell (7 June 1778 – 30 March 1840) was an important figure in Regency England and, for many years, the arbiter of men's fashion. At one time, he was a close friend of the Prince Regent, the future King George IV, but ...
(1776-1840), who set fashion at the London Court. It also saw the invention of blue jeans, a highly popular form of workers's costume, invented in 1853 by Jacob W. Davis who used metal rivets to strengthen blue denim work clothing in the California gold fields. The invention was funded by San Francisco entrepreneur Levi Strauss, and spread around the world. . File:Starry Night Over the Rhone.jpg, Van Gogh's '' Starry Night Over the Rhône'' (1888). Blue used to create a mood or atmosphere. A cobalt blue sky, and cobalt or ultramarine water. File:Old guitarist chicago.jpg, Blue conveys melancholy in
Picasso Pablo Ruiz Picasso (25 October 1881 – 8 April 1973) was a Spanish painter, sculptor, printmaker, ceramicist and Scenic design, theatre designer who spent most of his adult life in France. One of the most influential artists of the 20th ce ...
's '' The Old Guitarist'' (1903-1904). File:Matisse Conversation.jpg, "The Conversation" by Henri Matisse (1908-1912)
Recognizing the emotional power of blue, many artists made it the central element of paintings in the 19th and 20th centuries. They included Pablo Picasso, Pavel Kuznetsov and the Blue Rose art group, and Kandinsky and Der Blaue Reiter (The Blue Rider) school.Wassily Kandinsky, M. T. Sadler (Translator) ''Concerning the Spiritual in Art''. Dover Publ. (Paperback). 80 pp. . Henri Matisse expressed deep emotions with blue:, "A certain blue penetrates your soul." In the second half of the 20th century, painters of the abstract expressionist movement use blues to inspire ideas and emotions. Painter Mark Rothko observed that colour was "only an instrument;" his interest was "in expressing human emotions tragedy, ecstasy, doom, and so on."


In society and culture


Uniforms

File:Very friendly MPS officers in London.jpg, Officers of the London
Metropolitan Police The Metropolitan Police Service (MPS), formerly and still commonly known as the Metropolitan Police (and informally as the Met Police, the Met, Scotland Yard, or the Yard), is the territorial police force responsible for law enforcement and ...
File:Royal Navy Sailors on Parade MOD 45155635.jpg, Sailors of the Royal Navy File:2010. Донецк. Карнавал на день города 010.jpg, Ukrainian police officer in Donetsk
In the 17th century. The Prince-Elector of Brandenburg,
Frederick William I of Prussia Frederick William I (german: Friedrich Wilhelm I.; 14 August 1688 – 31 May 1740), known as the "Soldier King" (german: Soldatenkönig), was King in Prussia and Elector of Brandenburg from 1713 until his death in 1740, as well as Prince of Neuch ...
, chose
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyanid ...
as the new colour of Prussian military uniforms, because it was made with Woad, a local crop, rather than Indigo, which was produced by the colonies of Brandenburg's rival, England. It was worn by the German army until World War I, with the exception of the soldiers of Bavaria, who wore sky-blue. In 1748, the Royal Navy adopted a dark shade of blue for the uniform of officers.Heller (2010) p.32 It was first known as marine blue, now known as navy blue. The militia organized by
George Washington George Washington (February 22, 1732, 1799) was an American military officer, statesman, and Founding Father who served as the first president of the United States from 1789 to 1797. Appointed by the Continental Congress as commander of th ...
selected blue and buff, the colours of the British Whig Party. Blue continued to be the colour of the field uniform of the US Army until 1902, and is still the colour of the dress uniform. In the 19th century, police in the United Kingdom, including the
Metropolitan Police The Metropolitan Police Service (MPS), formerly and still commonly known as the Metropolitan Police (and informally as the Met Police, the Met, Scotland Yard, or the Yard), is the territorial police force responsible for law enforcement and ...
and the
City of London Police The City of London Police is the territorial police force responsible for law enforcement within the City of London, including the Middle and Inner Temples. The force responsible for law enforcement within the remainder of the London region, ou ...
also adopted a navy blue uniform. Similar traditions were embraced in France and Austria. It was also adopted at about the same time for the uniforms of the officers of the New York City Police Department.


Religion

File:Sri Mariamman Temple Singapore 2 amk.jpg, In Hinduism, Krishna is depicted with blue skin File:Reknown blue domes of the Church dedicated to St. Spirou in Firostefani, Santorini island (Thira), Greece.jpg, Blue domes of the Church dedicated to St. Spirou in Firostefani,
Santorini Santorini ( el, Σαντορίνη, ), officially Thira (Greek: Θήρα ) and classical Greek Thera (English pronunciation ), is an island in the southern Aegean Sea, about 200 km (120 mi) southeast from the Greek mainland. It is the ...
island (Thira), Greece. File:Mezquita Shah, Isfahán, Irán, 2016-09-20, DD 64.jpg, Persian blue in
Shah mosque The Shah Mosque ( fa, مسجد شاه) is a mosque located in Isfahan, Iran. It is located on the south side of Naghsh-e Jahan Square. It was built during the Safavid dynasty under the order of Shah Abbas I of Persia. It is regarded as one of ...
(16th c.) in
Isfahan Isfahan ( fa, اصفهان, Esfahân ), from its Achaemenid empire, ancient designation ''Aspadana'' and, later, ''Spahan'' in Sassanian Empire, middle Persian, rendered in English as ''Ispahan'', is a major city in the Greater Isfahan Regio ...
, Iran File:Flag-of-Israel-4-Zachi-Evenor.jpg, The flag of Israel uses a special variety of blue, called tekhelet
* Blue in Judaism: In the Torah, the Israelites were commanded to put fringes, '' tzitzit'', on the corners of their garments, and to weave within these fringes a "twisted thread of blue (''tekhelet'')". In ancient days, this blue thread was made from a dye extracted from a Mediterranean snail called the ''hilazon''. Maimonides claimed that this blue was the colour of "the clear noonday sky"; Rashi, the colour of the evening sky. According to several rabbinic sages, blue is the colour of God's Glory. Staring at this colour aids in mediation, bringing us a glimpse of the "pavement of sapphire, like the very sky for purity", which is a likeness of the Throne of God. (The Hebrew word for glory.) Many items in the '' Mishkan'', the portable sanctuary in the wilderness, such as the ''
menorah Menorah may refer to: * Jewish candelabra: ** Temple menorah, a seven-lamp candelabrum used in the ancient Tabernacle in the desert, the Temple in Jerusalem, and synagogues ** Hanukkah menorah or ''hanukkiyah'', a nine-lamp candelabrum used on the ...
'', many of the vessels, and the
Ark of the Covenant The Ark of the Covenant,; Ge'ez: also known as the Ark of the Testimony or the Ark of God, is an alleged artifact believed to be the most sacred relic of the Israelites, which is described as a wooden chest, covered in pure gold, with an e ...
, were covered with blue cloth when transported from place to place. * Blue in Christianity: Blue is particularly associated with the Virgin Mary. This was the result of a decree of Pope Gregory I (540-601) who ordered that all religious paintings should tell a story which was clearly comprehensible to all viewers, and that figures should be easily recognizable, especially that of the figure of Mary. If she was alone in the image, her costume was usually painted with the finest blue, ultramarine. If she was with Christ, her costume was usually painted with a less expensive pigment, to avoid outshining him.Heller, "Psychologie de la Colour - Effets et Symboliques", (2009),p. 32 * Blue in Hinduism: Many of the gods are depicted as having blue-coloured skin, particularly those associated with Vishnu, who is said to be the preserver of the world, and thus intimately connected to water. Krishna and Rama, Vishnu's avatars, are usually depicted with blue skin. Shiva, the destroyer deity, is also depicted in a light-blue hue, and is called ''neela kantha'', or blue-throated, for having swallowed poison to save the universe during the Samudra Manthana, the churning of the ocean of milk. Blue is used to symbolically represent the fifth, and the throat,
chakra Chakras (, ; sa , text=चक्र , translit=cakra , translit-std=IAST , lit=wheel, circle; pi, cakka) are various focal points used in a variety of ancient meditation practices, collectively denominated as Tantra, or the esoteric or ...
( Vishuddha). * Blue in Sikhism: The Akali Nihangs warriors wear all-blue attire.
Guru Gobind Singh Guru Gobind Singh (; 22 December 1666 – 7 October 1708), born Gobind Das or Gobind Rai the tenth Sikh Guru, a spiritual master, warrior, poet and philosopher. When his father, Guru Tegh Bahadur, was executed by Aurangzeb, Guru Gobind Sing ...
also has a
blue roan Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and " points"—lower legs, mane, and tail—are mostly solid-colored. Horses with roan coats have white hairs evenly ...
horse. The Sikh Rehat Maryada states that the Nishan Sahib hoisted outside every Gurudwara should be xanthic (Basanti in
Punjabi Punjabi, or Panjabi, most often refers to: * Something of, from, or related to Punjab, a region in India and Pakistan * Punjabi language * Punjabi people * Punjabi dialects and languages Punjabi may also refer to: * Punjabi (horse), a British Th ...
) or greyish blue (modern day navy blue) (Surmaaee in
Punjabi Punjabi, or Panjabi, most often refers to: * Something of, from, or related to Punjab, a region in India and Pakistan * Punjabi language * Punjabi people * Punjabi dialects and languages Punjabi may also refer to: * Punjabi (horse), a British Th ...
) colour. *Blue in
Paganism Paganism (from classical Latin ''pāgānus'' "rural", "rustic", later "civilian") is a term first used in the fourth century by early Christianity, early Christians for people in the Roman Empire who practiced polytheism, or ethnic religions ot ...
: Blue is associated with peace, truth, wisdom, protection, and patience. It helps with healing, psychic ability, harmony, and understanding.


Sports

File:Italy Team - Rome, 1965.jpg, The Italian national football team File:Serbia national volleyball team at the 2012 Summer Olympics (7913882066).jpg, Serbian national volleyball team, 2012 Olympics In sports, blue is widely represented in uniforms in part because the majority of national teams wear the colours of their national flag. For example, the World Cup-winning France are known as ''Les Bleus'' (the Blues). Similarly, Argentina, Italy, and Uruguay wear blue shirts. The Asian Football Confederation and the
Oceania Football Confederation The Oceania Football Confederation (OFC) is one of the six continental confederations of international association football. The OFC has 13 members, 11 of which are full members and two which are associate members not affiliated with FIFA. It ...
use blue text on their logos. Blue is well represented in baseball ( Blue Jays, basketball, and American football, and Ice hockey. The Indian national cricket team wears blue uniform during
One day international A One Day International (ODI) is a form of limited overs cricket, played between two teams with international status, in which each team faces a fixed number of overs, currently 50, with the game lasting up to 9 hours. The Cricket World C ...
matches, as such the team is also referred to as "Men in Blue".


Politics

File:Flag of the United Nations.svg, Flag of the United Nations, approximates "sky blue" File:Flag of Europe.svg, Flag of the European Union is "reflex blue", a medium dark blue File:Red state, blue state.svg, A presidential-election map of the US, 2004–2016. States that consistently vote for Democrats are termed "blue states". Unlike red or green, blue was not strongly associated with any particular country, religion or political movement. As the colour of harmony, it was chosen as the colour for the flags of the United Nations, the European Union, and NATO.Heller, "Psychologie de la Couleur" pp. 36-37 In politics, blue is sometimes used as the colour of conservative parties, contrasting with the red of more leftist parties. It is the colour of the British Conservative party. However, in the United States, the colours are reversed. To avoid associations of the Democrats with socialism or the far left, States which voted Democratic in four consecutive presidential elections are termed "blue states", while those which voted for Republicans are termed "red states". States which voted for different parties in two of the last four presidential elections are called "Swing States", and are usually coloured purple, a mix of red and blue, or sometimes pink or light blue.


See also

*
Engineer's blue Engineer's blue (also known as scraping blue, Prussian blue, or simply bluing) is a highly pigmented paste used to assist in the mating of two or more components. History Joseph Whitworth popularized the first practical method of making accurat ...
* Lists of colours * Non-photo blue * Blue pigments


References


Works cited

* (page numbers refer to the French translation) * * * * * * *


Further reading

* * * *


External links

* *
"Friday essay: from the Great Wave to Starry Night, how a blue pigment changed the world", By Dr Hugh Davies, theconversation.com
{{Authority control Primary colors Secondary colors Optical spectrum Rainbow colors Web colors