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Web colors are
color 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 ...
s used in displaying web pages on the
World Wide Web The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet. Documents and downloadable media are made available to the network through web se ...
, and the methods for describing and specifying those colors. Colors may be specified as an
RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
triplet or in
hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
format (a ''hex triplet'') or according to their common English names in some cases. A
color tool A color picker (also color chooser or color tool) is a graphical user interface widget, usually found within graphics software or online, used to select colors and, in some cases, to create color schemes (the color picker might be more sophis ...
or other
graphics software In computer graphics, graphics software refers to a program or collection of programs that enable a person to manipulate images or models visually on a computer. Computer graphics can be classified into two distinct categories: raster graphics a ...
is often used to generate color values. In some uses, hexadecimal color codes are specified with notation using a leading
number sign The symbol is known variously in English-speaking regions as the number sign, hash, or pound sign. The symbol has historically been used for a wide range of purposes including the designation of an ordinal number and as a Typographic ligature, ...
(#). A color is specified according to the intensity of its red, green and blue components, each represented by eight
bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
s. Thus, there are 24 bits used to specify a web color within the
sRGB sRGB is a standard RGB (red, green, blue) color space that HP and Microsoft created cooperatively in 1996 to use on monitors, printers, and the World Wide Web. It was subsequently standardized by the International Electrotechnical Commission ( ...
gamut, and 16,777,216 colors that may be so specified. Colors outside the sRGB gamut can be specified in
Cascading Style Sheets Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone techno ...
by making one or more of the red, green and blue components negative or greater than 100%, so the color space is theoretically an unbounded extrapolation of sRGB similar to
scRGB scRGB is a wide color gamut RGB color space created by Microsoft and HP that uses the same color primaries and white/black points as the sRGB color space but allows coordinates below zero and greater than one. The full range is −0.5 through ...
. Specifying a non-sRGB color this way requires the RGB() function call. It is impossible with the hexadecimal syntax (and thus impossible in legacy
HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...
documents that do not use CSS). The first versions of
Mosaic A mosaic is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster/mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and were particularly pop ...
and
Netscape Navigator Netscape Navigator was a web browser, and the original browser of the Netscape line, from versions 1 to 4.08, and 9.x. It was the flagship product of the Netscape Communications Corp and was the dominant web browser in terms of usage share in ...
used the
X11 color names In computing, on the X Window System, X11 color names are represented in a simple text file, which maps certain strings to RGB color values. It was traditionally shipped with every X11 installation, hence the name, and is usually located in ''<X ...
as the basis for their color lists, as both started as
X Window System The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wit ...
applications. Web colors have an unambiguous colorimetric definition,
sRGB sRGB is a standard RGB (red, green, blue) color space that HP and Microsoft created cooperatively in 1996 to use on monitors, printers, and the World Wide Web. It was subsequently standardized by the International Electrotechnical Commission ( ...
, which relates the chromaticities of a particular
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 ...
set, a given transfer curve, adaptive whitepoint, and viewing conditions. These have been chosen to be similar to many real-world
monitors Monitor or monitor may refer to: Places * Monitor, Alberta * Monitor, Indiana, town in the United States * Monitor, Kentucky * Monitor, Oregon, unincorporated community in the United States * Monitor, Washington * Monitor, Logan County, West Vir ...
and viewing conditions, to allow rendering to be fairly close to the specified values even without
color management In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printer ...
.
User agent In computing, a user agent is any software, acting on behalf of a user, which "retrieves, renders and facilitates end-user interaction with Web content". A user agent is therefore a special kind of software agent. Some prominent examples of us ...
s vary in the fidelity with which they represent the specified colors. More advanced user agents use color management to provide better color fidelity; this is particularly important for
Web-to-print Web-to-print, also known as Web2Print, remote publishing or print e-commerce is commercial printing using web sites. Companies and software solutions that deal in web-to-print use standard e-commerce and online services like hosting, website design ...
applications.


Hex triplet

A hex triplet is a six-digit, three-
byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
number used in
HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...
,
CSS Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone techno ...
, SVG, and other computing applications to represent colors. The bytes represent the red, green, and blue components of the color. One byte represents a number in the range 00 to FF (in hexadecimal notation), or 0 to 255 in decimal notation. This represents the least (0) to the most (255) intensity of each of the color components. Thus web colors specify colors in the 24-bit RGB color scheme. The hex triplet is formed by concatenating three bytes in hexadecimal notation, in the following order: *Byte 1: red value (color type red) *Byte 2: green value (color type green) *Byte 3: blue value (color type blue) For example, consider the color where the red/green/blue values are decimal numbers: red=36, green=104, blue=160 (a grayish-blue color). The decimal numbers 36, 104, and 160 are equivalent to the hexadecimal numbers 24, 68, and A0 respectively. The hex triplet is obtained by concatenating the six hexadecimal digits together, 2468A0 in this example. If any one of the three color values is less than 10 hex (16 decimal), it must be represented with a leading zero so that the triplet always has exactly six digits. For example, the decimal triplet 4, 8, 16 would be represented by the hex digits 04, 08, 10, forming the hex triplet 040810. The number of colors that can be represented by this system is 166 or 2563 or 224 = 16,777,216.


Shorthand hexadecimal form

An abbreviated, three (hexadecimal)-digit form is used. Expanding this form to the six-digit form is as simple as repeating each digit: 09C becomes 0099CC as presented on the following
CSS Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone techno ...
example: .threedigit .sixdigit /* same color as above */ This shorthand form reduces the palette to 4,096 colors, equivalent of 12-bit color as opposed to 24-bit color using the whole six-digit form (16,777,216 colors). This limitation is sufficient for many text-based documents.


Converting RGB to hexadecimal

RGB values are usually given in the 0–255 range; if they are in the 0–1 range, the values are multiplied by 255 before conversion. This number divided by sixteen (integer division; ignoring any remainder) gives the first hexadecimal digit (between 0 and F, where the letters A to F represent the numbers 10 to 15. See
hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
for more details). The remainder gives the second hexadecimal digit. For instance, the RGB value 201 divides into 12 groups of 16, thus the first digit is C. A remainder of nine gives the hexadecimal number C9. This process is repeated for each of the three color values. Conversion between number bases is a common feature of calculators, including both hand-held models and the software calculators bundled with most modern
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s. Web-based tools specifically for converting color values are also available.


HTML color names

Recent
W3C The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 and led by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working to ...
specifications of color names distinguishes between ''basic'' and ''extended'' colors. In HTML and XHTML, colors can be used for text, background color, frame borders, tables, and individual table cells.


Basic colors

The basic colors are 16 colors defined in the
HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...
4.01 specification, ratified in 1999, as follows (names are defined in this context to be case-insensitive): These 16 were labelled as sRGB and included in the HTML 3.0 specification, which noted they were "the standard 16 colors supported with the Windows
VGA Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the PC industry within three years. The term can no ...
palette."


Extended colors

Extended colors are the result of merging specifications from HTML 4.01, CSS 2.0, SVG 1.0 and CSS3 User Interfaces (CSS3 UI). Several colors are defined by
web browser A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used on ...
s. A particular browser may not recognize all of these colors, but as of 2005, all modern, general-use, graphical browsers support the full list of colors. Many of these colors are from the list of
X11 color names In computing, on the X Window System, X11 color names are represented in a simple text file, which maps certain strings to RGB color values. It was traditionally shipped with every X11 installation, hence the name, and is usually located in ''<X ...
distributed with the
X Window System The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wit ...
. These colors were standardized by SVG 1.0, and are accepted by SVG Full user agents. They are not part of SVG Tiny. The list of colors shipped with the X11 product varies between implementations and clashes with certain of the HTML names such as green. X11 colors are defined as simple
RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
(hence, no particular color space), rather than
sRGB sRGB is a standard RGB (red, green, blue) color space that HP and Microsoft created cooperatively in 1996 to use on monitors, printers, and the World Wide Web. It was subsequently standardized by the International Electrotechnical Commission ( ...
. This means that the list of colors found in X11 (e.g., in /usr/lib/X11/rgb.txt) should not directly be used to choose colors for the web. The list of web "X11 colors" from the CSS3 specification, along with their hexadecimal and decimal equivalents, is shown below. Compare the alphabetical lists in the W3C standards. This includes the common synonyms: aqua (HTML4/CSS 1.0 standard name) and cyan (common sRGB name),
magenta Magenta () is a color that is variously defined as pinkish- purplish-red, reddish-purplish-pink or mauvish-crimson. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located exactly midway between red and blue. I ...
(common sRGB name) and fuchsia (HTML4/CSS 1.0 standard name), gray (HTML4/CSS 1.0 standard name) and grey.


CSS colors

The
Cascading Style Sheets Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone techno ...
specification defines the same number of named colors as the HTML 4 spec, namely the 16 html colors, and 124 colors from the Netscape X11 color list for a total of 140 names that were recognized by Internet Explorer (IE) 3.0 and Netscape Navigator 3.0. Blooberry.com notes that Opera 2.1 and Safari 1 also included Netscape's expanded list of 140 color names, but later discovered 14 names not included with Opera 3.5 on Windows 98. In CSS 2.1, the color 'orange' (one of the 140) was added to the section with the 16 HTML4 colors as a 17th color. The CSS3.0 specification did not include ''orange'' in the "HTML4 color keywords" section, which was renamed as "Basic color keywords". In the same reference, the "SVG color keywords" section, was renamed "Extended color keywords", after starting out as "X11 color keywords" in an earlier working draft. The working draft for the level 4 color module combines the Basic and Extended sections together in a simple "Named Colors" section.CSS Color Module Level 4 Editor's Draft, 26 June 2014
/ref>
CSS 2, SVG and CSS 2.1 allow web authors to use ''system colors'', which are color names whose values are taken from the
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
, picking the operating system's highlighted text color, or the background color for tooltip controls. This enables web authors to style their content in line with the operating system of the user agent. The
CSS3 Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as Scalable Vector Graphics, SVG, MathML or XHTML). CS ...
color module has
deprecated In several fields, especially computing, deprecation is the discouragement of use of some terminology, feature, design, or practice, typically because it has been superseded or is no longer considered efficient or safe, without completely removing ...
the use of system colors in favor of CSS3 UI System Appearance property, which itself was subsequently dropped from CSS3. The CSS3 specification also introduces
HSL color space HSL (for hue, saturation, lightness) and HSV (for hue, saturation, value; also known as HSB, for hue, saturation, brightness) are alternative representations of the RGB color model, designed in the 1970s by computer graphics researchers to more ...
values to style sheets: /* RGB model */ p /* #rgb */ p /* #rrggbb */ p /* integer range 0 - 255 */ p /* float range 0.0% - 100.0% */ /* RGB with alpha channel, added to CSS3 */ p /* 0.5 opacity, semi-transparent */ /* HSL model, added to CSS3 */ p /* red */ p /* green */ p /* dark green */ p /* light green */ p /* pastel green */ /* HSL model with alpha channel */ p /* green */ p /* semi-transparent green */ p /* very transparent green */ CSS also supports the special color transparent, which represents an alpha value of zero; by default, transparent is rendered as an invisible nominal black: rgba(0, 0, 0, 0). It was introduced in CSS1 but its scope of use has expanded over the versions.


CSS Color 4

Level 4 of the CSS Color specification introduced several new CSS color formats. Besides new ways to write colors, it also introduces the concept of mixing colors in a non-sRGB color space, a first step towards fixing a well-known issue in color gradients. Some sections explaining color theory and common operations like
gamut mapping In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printe ...
are also added to aid implementation.


Device independent color

CSS Color 4 introduces several different formats for device independent color that can display the entirety of visible color (in a capable screen), including: * Lab and LCH * OKLab and OKLCH (preferred over Lab/LCH) * XYZ (D50 or D65 efault


Predefined color spaces

A number of
RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
spaces with gamuts that are wider than
sRGB sRGB is a standard RGB (red, green, blue) color space that HP and Microsoft created cooperatively in 1996 to use on monitors, printers, and the World Wide Web. It was subsequently standardized by the International Electrotechnical Commission ( ...
are also introduced through the new color() function: *
Display P3 P3 is an RGB color space. DCI-P3 (Digital Cinema Initiative) is used with digital theatrical motion picture distribution (DCDM). Display P3 is a variant developed by Apple Inc. for wide-gamut displays. __TOC__ History Development of the stand ...
* Prophoto *
REC.2020 ITU-R Recommendation BT.2020, more commonly known by the abbreviations Rec. 2020 or BT.2020, defines various aspects of ultra-high-definition television (UHDTV) with standard dynamic range (SDR) and wide color gamut (WCG), including picture ...
* Adobe 1998 RGB A linearized variant of sRGB is also defined for color mixing.


Other formats

On 21 June 2014, the CSS WG added the color RebeccaPurple to the Editor's Draft of the Colors module level 4, to commemorate Eric Meyer's daughter Rebecca, who died on 7 June 2014, her sixth birthday.
CSS4 also introduces the
HWB color model HWB (Hue, Whiteness, Blackness) is a cylindrical-coordinate representation of points in an RGB color model, similar to HSL and HSV. It was developed by HSV’s creator Alvy Ray Smith in 1996 to address some of the issues with HSV. HWB was designed ...
as an alternative to HSL/HSV.


CSS Color 5

The draft CSS Color 5CSS Color Module Level 5
/ref> specification introduces syntax for mixing and manipulating existing colors, including: * A color-mix() function for mixing colors * Relative color syntax for manipulating components of an existing color Custom color spaces are also supported via
ICC profile In color management, an ICC profile is a set of data that characterizes a color input or output device, or a color space, according to standards promulgated by the International Color Consortium (ICC). Profiles describe the color attributes of a ...
s. This allows the use of
CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
on web pages.


Web-safe colors

In the mid-1990s, many displays were only capable of displaying 256 colors. These may be dictated by the hardware or changeable by a "color table". When a color is found (e.g., in an image) that is not available, a different one had to be used. This can be done by either using the closest color or by using
dither Dither is an intentionally applied form of image noise, noise used to randomize quantization error, preventing large-scale patterns such as color banding in images. Dither is routinely used in processing of both digital audio and digital vide ...
ing. There were various attempts to make a "standard" color palette. A set of colors was needed that could be shown without dithering on 256-color displays; the number 216 was chosen partly because computer operating systems customarily reserved sixteen to twenty colors for their own use; it was also selected because it allows exactly six equally spaced shades of red, green, and blue (6 × 6 × 6 = 216), each from 00 to FF (including both limits). The list of colors is presented as if it had special properties that render them immune to dithering, but on 256-color displays applications can actually set a palette of any selection of colors that they choose, dithering the rest. These colors were chosen specifically because they matched the palettes selected by various browser applications. There were not very different palettes in use in different browsers. "Web-safe" colors had a flaw in that, on systems such as
X11 The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wi ...
where the palette is shared between applications, smaller color cubes (5×5×5 or 4×4×4) were allocated by browsers—the "web-safe" colors would dither on such systems. Different results were obtained by providing an image with a larger range of colors and allowing the browser to quantize the color space if needed, rather than suffer the quality loss of a double quantization. Through the 2000s, use of 256-color displays in personal computers dropped sharply in favour of 24-bit ( TrueColor) displays, and the use of "web-safe" colors has fallen into practical disuse. The "web-safe" colors do not all have standard names, but each can be specified by an
RGB The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three addi ...
triplet: each component (red, green, and blue) takes one of the six values from the following table (out of the 256 possible values available for each component in full 24-bit color). The following table shows all of the "web-safe" colors. One shortcoming of the web-safe palette is its small range of light colors for webpage backgrounds, whereas the intensities at the low end of the range, such as the two darkest, are similar to each other, making them hard to distinguish. Values flanked by "*" (asterisk) are part of the "really safe palette;" see Safest web colors, below.


Color table


Safest web colors

Designers were encouraged to stick to these 216 "web-safe" colors in their websites because there were a lot of 8-bit color displays when the 216-color palette was developed. David Lehn and Hadley Stern discovered that only 22 of the 216 colors in the web-safe palette are reliably displayed without inconsistent remapping on 16-bit computer displays. They called these 22 colors "the really safe palette"; it consists largely of shades of green, yellow, and blue.


Accessibility


Color selection

Some
browsers Browse, browser or browsing may refer to: Programs * Web browser, a program used to access the World Wide Web *Code browser, a program for navigating source code * File browser or file manager, a program used to manage files and related objects * ...
and devices do not support colors. For these displays or blind and colorblind users, Web content depending on colors can be unusable or difficult to use. Either no colors should be specified (to invoke the browser's default colors), or both the background and all foreground colors (such as the colors of plain text, unvisited links, hovered links, active links, and visited links) should be specified to avoid black on black or white on white effects.


Color contrast

The
Web Content Accessibility Guidelines The Web Content Accessibility Guidelines (WCAG) are part of a series of web accessibility guidelines published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C), the main international standards organization for ...
recommend a contrast ratio of at least 4.5:1 between the
relative luminance Relative luminance Y follows the photometric definition of luminance L including spectral weighting for human vision, but while luminance L is a measure of light in units such as cd/m^2, Relative luminance Y values are normalized as 0.0 to 1.0 ...
of text and its background color or at least 3:1 for large text. Enhanced accessibility requires contrast ratios greater than 7:1. However, addressing accessibility concerns is not simply a matter of increasing the contrast ratio. As a report to the
Web Accessibility Initiative The World Wide Web Consortium (W3C)'s Web Accessibility Initiative (WAI) is an effort to improve the accessibility of the World Wide Web (WWW or Web) for people with disabilities. People with disabilities may encounter difficulties when using com ...
indicates,Optimal Colors to Improve Readability for People with Dyslexia
/ref>
dyslexic Dyslexia, also known until the 1960s as word blindness, is a disorder characterized by reading below the expected level for one's age. Different people are affected to different degrees. Problems may include difficulties in spelling words, r ...
readers are better served by contrast ratios below the maximum. The recommendations they refer to of off-black (#0A0A0A) on off-white (#FFFFE5) and black (#000000) on creme (#FAFAC8) have contrast ratios of 11.7:1 and 20.3:1 respectively. Among their other color pairs, brown (#282800) on dark green (#A0A000) has a contrast ratio of 3.24:1, which is less than the
WCAG The Web Content Accessibility Guidelines (WCAG) are part of a series of web accessibility guidelines published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C), the main international standards organization for th ...
recommendation, dark brown (#1E1E00) on light green (#B9B900) has a contrast ratio of 4.54:1 and blue (#00007D) on yellow (#FFFF00) has a contrast ratio of 11.4:1. Notice that the colors named in the report use different color values than the web colors of the same name.


See also


References


External links


CSS color value
on
MDN Web Docs MDN Web Docs, previously Mozilla Developer Network and formerly Mozilla Developer Center, is a documentation repository and learning resource for web developers. It was started by Mozilla in 2005 as a unified place for documentation about open web ...

CSS2.1 Color Specification
* {{Color topics, state=collapsed Color Web design Articles with example code