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Impossible colors are colors that do not appear in ordinary visual functioning. Different color theories suggest different hypothetical colors that humans are incapable of perceiving for one reason or another, and fictional colors are routinely created in popular culture. While some such colors have no basis in reality, phenomena such as cone cell fatigue enable colors to be perceived in certain circumstances that would not be otherwise.


Opponent process

The color opponent process is a color theory that states that the human visual system interprets information about color by processing signals from cone and rod cells in an antagonistic manner. The three types of
cone cell Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cone ...
s have some overlap in the wavelengths of light to which they respond, so it is more efficient for the visual system to record differences between the responses of cones, rather than each type of cone's individual response. The opponent color theory suggests that there are three opponent channels: * Red versus green * Blue versus yellow * Black versus white (this is achromatic and detects light–dark variation or luminance) Responses to one color of an opponent channel are antagonistic to those to the other color, and signals output from a place on the retina can contain one or the other but not both, for each opponent pair.


Imaginary colors

A ''fictitious color'' or ''imaginary color'' is a point in a
color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represent ...
that corresponds to combinations of
cone cell Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cone ...
responses in one eye that cannot be produced by the eye in normal circumstances seeing any possible light spectrum. No physical object can have an imaginary color. The
spectral sensitivity Spectral sensitivity is the relative efficiency of detection, of light or other signal, as a function of the frequency or wavelength of the signal. In visual neuroscience, spectral sensitivity is used to describe the different characteristics o ...
curve of medium-wavelength ("M") cone cells overlaps those of short-wavelength ("S") and long-wavelength ("L") cone cells. Light of any
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
that interacts with M cones also interacts with S or L cones, or both, to some extent. Therefore, no wavelength and no
spectral power distribution In radiometry, photometry, and color science, a spectral power distribution (SPD) measurement describes the power per unit area per unit wavelength of an illumination (radiant exitance). More generally, the term ''spectral power distribution'' ...
excites only one sort of cone. If, for example, M cones could be excited alone, this would make the brain see an imaginary color greener than any physically possible green. Such a "hyper-green" color would be in the
CIE 1931 color space The CIE 1931 color spaces are the first defined quantitative links between distributions of wavelengths in the electromagnetic visible spectrum, and physiologically perceived colors in human color vision. The mathematical relationships that defin ...
chromaticity diagram in the blank area above the colored area and between the ''y''-axis and the line ''x''+''y''=1.


Imaginary colors in color spaces

Although they cannot be seen, imaginary colors are often found in the mathematical descriptions that define
color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represent ...
s. Any additive mixture of two real colors is also a real color. When colors are displayed in the CIE 1931 XYZ color space, additive mixture results in color along the line between the colors being mixed. By mixing any three colors, one can therefore create any color contained in the triangle they describe—this is called the
gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
formed by those three colors, which are called
primary color A set (mathematics), set of primary colors or primary colours (see American and British English spelling differences#-our, -or, spelling differences) consists of colorants or colored lights that can be mixed in varying amounts to produce a gamu ...
s. Any colors outside of this triangle cannot be obtained by mixing the chosen primaries. When defining primaries, the goal is often to leave as many real colors in gamut as possible. Since the region of real colors is not a triangle (see illustration), it is not possible to pick three real colors that span the whole region. The gamut can be increased by selecting more than three real primary colors, but since the region of real colors is not a polygon, there will always be some colors at the edge left out. Therefore, one selects colors outside of the region of real colors as primary colors; in other words, imaginary or fictitious primary colors. Mathematically, the gamut created in this way contains so-called imaginary or fictitious colors. In computer and television screen color displays, the corners of the gamut triangle are defined by commercially available
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or vi ...
s chosen to be as near as possible to pure red, and pure green, and pure blue, and thus are within the area of real colors; note that these color space diagrams inevitably display, instead of real colors outside your computer screen's gamut triangle, the nearest color which is inside the gamut triangle. See page
Gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
for more information about the color range available on display devices.


Chimerical colors

A ''chimerical color'' is an imaginary color that can be seen temporarily by looking steadily at a strong color until some of the cone cells become fatigued, temporarily changing their color sensitivities, and then looking at a markedly different color. The direct
trichromatic Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal expl ...
description of vision cannot explain these colors, which can involve
saturation Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds **Saturated and unsaturated compounds ** Degree of unsaturation **Saturated fat or fatty aci ...
signals outside the physical
gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
imposed by the trichromatic model.
Opponent process The opponent process is a color theory that states that the human visual system interprets information about color by processing signals from photoreceptor cells in an antagonistic manner. The opponent-process theory suggests that there are thr ...
color theories, which treat intensity and chroma as separate visual signals, provide a biophysical explanation of these chimerical colors. For example, staring at a saturated primary-color field and then looking at a white object results in an opposing shift in hue, causing an
afterimage AfterImage is a Filipino rock band formed in 1986, best known for their songs "Habang May Buhay", "Next in Line", and "Mangarap Ka". They disbanded in 1997 and became active again in 2008 after they reunited and released their fourth studio album ...
of the
complementary color Complementary colors are pairs of colors which, when combined or mixed, cancel each other out (lose hue) by producing a grayscale color like white or black. When placed next to each other, they create the strongest contrast for those two co ...
. Exploration of the color space outside the range of "real colors" by this means is major corroborating evidence for the opponent-process theory of color vision. Chimerical colors can be seen while seeing with one eye or with both eyes, and are not observed to reproduce simultaneously qualities of opposing colors (e.g. "yellowish blue"). Chimerical colors include: * Stygian colors: these are simultaneously dark and impossibly saturated. For example, to see "stygian blue": staring at bright yellow causes a dark blue
afterimage AfterImage is a Filipino rock band formed in 1986, best known for their songs "Habang May Buhay", "Next in Line", and "Mangarap Ka". They disbanded in 1997 and became active again in 2008 after they reunited and released their fourth studio album ...
, then on looking at black, the blue is seen as blue against the black, also as dark as the black. The color is not possible to achieve through normal vision, because the lack of incident light (in the black) prevents saturation of the blue/yellow chromatic signal (the blue appearance). * Self-luminous colors: these mimic the effect of glowing material, even when viewed on a medium such as paper, which can only reflect and not emit its own light. For example, to see "self-luminous red": staring at green causes a red afterimage, then on looking at white, the red is seen against the white and may seem to be brighter than the white. * Hyperbolic colors: these are impossibly highly saturated. For example, to see "hyperbolic orange": staring at bright cyan causes an orange afterimage, then on looking at orange, the resulting orange afterimage seen against the orange background may cause an orange color purer than the purest orange color that can be made by any normally-seen light.


Claimed evidence for the ability to see colors not in the color space

According to the opponent-process theory, under normal circumstances, there is no hue that could be described as a mixture of opponent hues; that is, as a hue looking "redgreen" or "yellowblue". In 1983, Hewitt D. Crane and Thomas P. Piantanida performed tests using an eye-tracker device that had a field of a vertical red stripe adjacent to a vertical green stripe, or several narrow alternating red and green stripes (or in some cases, yellow and blue instead). The device could track involuntary movements of one eye (there was a patch over the other eye) and adjust mirrors so the image would follow the eye and the boundaries of the stripes were always on the same places on the eye's retina; the field outside the stripes was blanked with occluders. Under such conditions, the edges between the stripes seemed to disappear (perhaps due to edge-detecting
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s becoming fatigued) and the colors flowed into each other in the brain's
visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
, overriding the opponency mechanisms and producing not the color expected from mixing paints or from mixing lights on a screen, but new colors entirely, which are not in the
CIE 1931 color space The CIE 1931 color spaces are the first defined quantitative links between distributions of wavelengths in the electromagnetic visible spectrum, and physiologically perceived colors in human color vision. The mathematical relationships that defin ...
, either in its real part or in its imaginary parts. For red-and-green, some saw an even field of the new color; some saw a regular pattern of just-visible green dots and red dots; some saw islands of one color on a background of the other color. Some of the volunteers for the experiment reported that afterward, they could still imagine the new colors for a period of time.
Some observers indicated that although they were aware that what they were viewing was a color (that is, the field was not achromatic), they were unable to name or describe the color. One of these observers was an artist with large color vocabulary. Other observers of the novel hues described the first stimulus as a reddish-green.
In 2001, Vincent A. Billock and Gerald A. Gleason and Brian H. Tsou set up an experiment to test a theory that the 1983 experiment did not control for variations in the perceived
luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...
of the colors from subject to subject: two colors are equiluminant for an observer when rapidly alternating between the colors produces the least impression of flickering. The 2001 experiment was similar but controlled for luminance. They had these observations:
Some subjects (4 out of 7) described transparency phenomena—as though the opponent colors originated in two depth planes and could be seen, one through the other. ... We found that when colors were equiluminant, subjects saw reddish greens, bluish yellows, or a multistable spatial color exchange (an entirely novel perceptual phenomena ); when the colors were nonequiluminant, subjects saw spurious pattern formation.
This led them to propose a "soft-wired model of cortical color opponency", in which populations of neurons compete to fire and in which the "losing" neurons go completely silent. In this model, eliminating competition by, for instance, inhibiting connections between neural populations can allow mutually exclusive neurons to fire together. Hsieh and Tse in 2006 disputed the existence of colors forbidden by opponency theory and claimed they are, in reality, intermediate colors. However, by their own account their methods differed from Crane and Piantanida: "They stabilized the border between two colors on the retina using an eye tracker linked to deflector mirrors, whereas we relied on visual fixation." Hsieh and Tse do not compare their methods to Billock and Tsou, and do not cite their work, even though it was published five years earlier in 2001. See also
binocular rivalry Binocular rivalry is a phenomenon of visual perception in which perception alternates between different images presented to each eye. When one image is presented to one eye and a very different image is presented to the other (also known as dich ...
.


In fiction

Some works of fiction have mentioned fictional colors outside of the normal human visual spectrum that have not been observed yet, and whose observation may require advanced technology, different physics or magic. Introduction of a new color is often an
allegory As a literary device or artistic form, an allegory is a narrative or visual representation in which a character, place, or event can be interpreted to represent a hidden meaning with moral or political significance. Authors have used allegory th ...
intending to deliver additional information to the reader. Such colors are primarily discussed in literary works, as they are currently impossible to visualize (when a new color is shown in the episode "
Reincarnation Reincarnation, also known as rebirth or transmigration, is the philosophical or religious concept that the non-physical essence of a living being begins a new life in a different physical form or body after biological death. Resurrection is a ...
" of the animated show ''
Futurama ''Futurama'' is an American animated science fiction sitcom created by Matt Groening for the Fox Broadcasting Company. The series follows the adventures of the professional slacker Philip J. Fry, who is cryogenically preserved for 1000 years a ...
'', the animation for that fragment of the show is purposely kept in shades of gray). Two of the earliest examples of fictional colors comes from the classic 1920
science fiction Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel unive ...
novel ''
A Voyage to Arcturus ''A Voyage to Arcturus'' is a novel by the Scottish writer David Lindsay, first published in 1920. An interstellar voyage is the framework for a narrative of a journey through fantastic landscapes. The story is set at Tormance, an imaginary pl ...
'', by David Lindsay, which mentions two new primary colors, "ulfire" and "jale". ''
The Colour Out of Space "The Colour Out of Space" is a science fiction/horror short story by American author H. P. Lovecraft, written in March 1927. In the tale, an unnamed narrator pieces together the story of an area known by the locals as the "blasted heath" ...
'', a 1927 story by H.P. Lovecraft, is named after an otherwise unnamed color, usually not observable by humans, generated by alien entities. Philip K. Dick's 1969 novel '' Galactic Pot-Healer'' mentions a color "rej",
Terry Pratchett Sir Terence David John Pratchett (28 April 1948 – 12 March 2015) was an English humourist, satirist, and author of fantasy novels, especially comical works. He is best known for his ''Discworld'' series of 41 novels. Pratchett's first nov ...
in his
Discworld ''Discworld'' is a comic fantasy"Humorous Fantasy" in David Pringle, ed., ''The Ultimate Encyclopedia of Fantasy'' (pp.31-33). London, Carlton,2006. book series written by the English author Terry Pratchett, set on the Discworld, a flat pla ...
series that began with ''
The Colour of Magic ''The Colour of Magic'' is a 1983 fantasy comedy novel by Terry Pratchett, and is the first book of the ''Discworld'' series. The first printing of the British edition consisted of only 506 copies. Pratchett has described it as "an attempt to ...
'' (1983) describes "
octarine The Discworld is the fictional setting for all of Terry Pratchett's ''Discworld'' fantasy novels. It consists of a large disc (complete with edge-of-the-world drop-off and consequent waterfall) resting on the backs of four huge elephants which ar ...
", a color that can be only seen by magicians and cats; and
Marion Zimmer Bradley Marion Eleanor Zimmer Bradley (June 3, 1930 – September 25, 1999) was an American author of fantasy, historical fantasy, science fiction, and science fantasy novels, and is best known for the Arthurian fiction novel ''The Mists of Avalon'' an ...
in her novel ''
The Colors of Space ''The Colors of Space'' is a 1963 science fiction novel by Marion Zimmer Bradley. The book has been reviewed by P. Schuyler Miller for the '' Analog Science Fiction and Fact'' (1964), by Steve Miller for the ''Science Fiction Review'' (1983), ...
'' (1963) mentions "the eighth color" made visible during the FTL travel. Brazilian writer
Ziraldo Ziraldo Alves Pinto (born October 24, 1932), usually referred to mononymous person, mononymically as Ziraldo, is a Brazilian author, painter, comic creator, and journalist. His books have sold about ten million copies, have been translated to ma ...
's 1969 children's book '' Flicts'' tells the story of a color of the same name (represented as an earthy shade of beige) that is segregated by the other colors found in the rainbow, flags and elsewhere, because Flicts is rare, seen as uncharacteristic, and therefore undervalued; at the end of the book, Flicts finds its place as the color of the moon (after being gifted an English copy of the book,
Neil Armstrong Neil Alden Armstrong (August 5, 1930 – August 25, 2012) was an American astronaut and aeronautical engineer who became the first person to walk on the Moon in 1969. He was also a naval aviator, test pilot, and university professor. ...
signed it and wrote "The moon is flicts"). "Pleurigloss" is the favorite color of the immortal afterlife being Michael from the television show ''
The Good Place ''The Good Place'' is an American fantasy comedy television series created by Michael Schur. It premiered on NBC on September 19, 2016, and concluded on January 30, 2020, after four seasons and 53 episodes. Although the plot evolves significa ...
''. In the show, pleurigloss is described as "the color of when a soldier comes home from war and sees his dog for the first time."
Vernor Vinge Vernor Steffen Vinge (; born October 2, 1944) is an American science fiction author and retired professor. He taught mathematics and computer science at San Diego State University. He is the first wide-scale popularizer of the technological singu ...
's science fiction novel ''
A Deepness in the Sky ''A Deepness in the Sky'' is a science fiction novel by American writer Vernor Vinge. Published in 1999, the novel is a loose prequel (set twenty thousand years earlier) to his earlier novel ''A Fire Upon the Deep'' (1992). The title is coined by ...
'' includes a species who can see a color whose name is translated as "plaid" (including a reference to "alpha plaid"). In ''
Fallen London ''Fallen London'', originally ''Echo Bazaar'', is a browser-based game, browser-based interactive narrative game developed by Failbetter Games and set in "Fallen London", an alternative Victorian era, Victorian London with gothic fiction, gothi ...
'', ''
Sunless Sea ''Sunless Sea'' is a survival/exploration role-playing video game with roguelike elements developed by Failbetter Games. The game was released on 6 February 2015 for Windows and OS X following a successful Kickstarter campaign to crowdfund the ...
'', and '' Sunless Skies'', which take place in a shared universe created by
Failbetter Games Failbetter Games is a British video game developer and interactive fiction studio based in London. History Founded in 2009 by Alexis Kennedy and Paul Arendt, Failbetter is chiefly known for its '' Fallen London'' Victorian Gothic franchise ...
, there exists seven colors as part of a "Neathbow" that cannot be viewed in plain sunlight, are counterparts to regular colors, and have fantastical properties, such as irrigo and violant, which remove and reinforce memories, respectively.


See also

*: in theatre lighting, typically in a
color gel Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
, a color blended with small amounts of complementary colors. * * *, an image that depicts an object in colors that differ from those that a visible-colors-only photograph would show. *, a shade of gray used to adjust photographs to match perceptual brightness as opposed to absolute brightness as measured by a digital camera. *Non-visible
electromagnetic wave In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
s, such as
radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...
s,
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
s,
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
s, etc. *''
Shades of Grey Variations of gray or grey include achromatic grayscale shades, which lie exactly between white and black, and nearby colors with low colorfulness. A selection of a number of these various colors is shown below. Chart of computer web color ...
'' – 2009 novel by Jasper Fforde, a novel where social class is determined by the specific colors that one can see * *, having four primary colors


References


Further reading

* * *


External links

* {{DEFAULTSORT:Impossible Colors Color Vision Perception