Web colors are colors used in displaying web pages on the World Wide Web; they can be described by way of three methods: a color may be specified as an RGB triplet, in hexadecimal format (a hex triplet) or according to its common English name in some cases. A color tool or other graphics software is often used to generate color values. In some uses, hexadecimal color codes are specified with notation using a leading number sign (#).[1][2] A color is specified according to the intensity of its red, green and blue components, each represented by eight bits. Thus, there are 24 bits used to specify a web color within the sRGB gamut, and 16,777,216 colors that may be so specified.
Colors outside the sRGB gamut can be specified in Cascading Style Sheets 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.[3] 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 documents that do not use CSS).
The first versions of Mosaic and Netscape Navigator used the X11 color names as the basis for their color lists, as both started as X Window System applications. Web colors have an unambiguous colorimetric definition, sRGB, which relates the chromaticities of a particular phosphor set, a given transfer curve, adaptive whitepoint, and viewing conditions.[4] These have been chosen to be similar to many real-world monitors and viewing conditions, to allow rendering to be fairly close to the specified values even without color management. User agents 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 applications.
Hex triplet
A hex triplet is a six-digit (or eight-digit), three-byte (or four-byte) hexadecimal number used in HTML, CSS, SVG, and other computing applications to represent colors. The bytes represent the red, green, and blue components of the color. The optional fourth byte refers to alpha channel. 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)
Byte 4 (optional): alpha value
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 or four-digit form can be used,[5] but can cause errors if software or maintenance scripts are only expecting the long form. Expanding this form to the six-digit form is as simple as repeating each digit: 09C becomes 0099CC as presented on the following CSS example:
.threedigit{color:#09C;}.sixdigit{color:#0099CC;}/* 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.
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 for more details). The remainder gives the second hexadecimal digit. For instance, the RGB value 58 divides into 3 groups of 16, thus the first digit is 3. A remainder of ten gives the hexadecimal number 3A. Likewise, 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 systems. Web-based tools specifically for converting color values are also available.
HTML color names
Recent W3C specifications of color names distinguishes between basic and extended colors.[6] In HTML and XHTML, colors can be used for text, background color, frame borders, tables, and individual table cells.[7]
Basic colors
The basic colors are 16 colors defined in the HTML 4.01 specification, ratified in 1999,[8] 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 palette."[9]
Extended colors
SVG Version of X11 color namesSVG1.1 named colors with sRGB hex/dec and HSL codes, at UHD (4K) resolution
Extended colors are the result of merging specifications from HTML 4.01, CSS 2.0, SVG 1.0 and CSS3 User Interfaces (CSS3 UI).[6]
Several colors are defined by web browsers. 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 distributed with the X Window System. 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 (hence, no particular color space), rather than sRGB. 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.[10]
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), fuchsia (HTML4/CSS 1.0 standard name) and magenta (common sRGB name), gray (HTML4/CSS 1.0 standard name) and grey.[11][12]
The Cascading Style Sheets 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.[13] 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.[14]
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.[15] The CSS3.0 specification did not include orange in the "HTML4 color keywords" section, which was renamed as "Basic color keywords".[16] 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.[17] The working draft for the level 4 color module combines the Basic and Extended sections together in a simple "Named Colors" section.[18]
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, 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.[19] The CSS3 color module has deprecated the use of system colors in favor of CSS3 UI System Appearance property,[20][21] which itself was subsequently dropped from CSS3.[22]
Example system color keywords
Appearance
Keyword
linkText
visitedText
activeText
highlight
mark
The CSS3 specification also introduces HSL color space values to style sheets:[23]
/* RGB model */p{color:#F00}/* #rgb */p{color:#FF0000}/* #rrggbb */p{color:rgb(255,0,0)}/* integer range 0 - 255 */p{color:rgb(100%,0%,0%)}/* float range 0.0% - 100.0% *//* RGB with alpha channel, added to CSS3 */p{color:rgba(255,0,0,0.5)}/* 0.5 opacity, semi-transparent *//* HSL model, added to CSS3 */p{color:hsl(0,100%,50%)}/* red */p{color:hsl(120,100%,50%)}/* green */p{color:hsl(120,100%,25%)}/* dark green */p{color:hsl(120,100%,75%)}/* light green */p{color:hsl(120,50%,50%)}/* pastel green *//* HSL model with alpha channel */p{color:hsla(120,100%,50%,1)}/* green */p{color:hsla(120,100%,50%,0.5)}/* semi-transparent green */p{color:hsla(120,100%,50%,0.1)}/* 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.[23]
CSS Color 4
Level 4 of the CSS Color specification introduced several new CSS color formats.[24]
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 are also added to aid implementation.[24]
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:[25]
A linearized variant of sRGB is also defined for color mixing.[24]
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.[26]
In the mid-1990s, many displays were only capable of displaying 256 colors,[28] dictated by the hardware or changeable by a "color table". When a color was found (e.g., in an image) that was not available, a different one had to be used. This was done by either using the closest color or by using dithering.
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 allowed 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 was presented as if it had special properties that render it immune to dithering, but on 256-color displays applications could actually set a palette of any selection of colors that they chose, 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.[citation needed]
"Web-safe" colors had a flaw in that, on systems such as X11 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,[29] 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 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).
6 shades of each color
Key
Hex
Decimal
Fraction
0
00
0
0
3
33
51
0.2
6
66
102
0.4
9
99
153
0.6
C (12)
CC
204
0.8
F (15)
FF
255
1
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
216 "web-safe" colors
*000*
300
600
900
C00
*F00*
*003*
303
603
903
C03
*F03*
006
306
606
906
C06
F06
009
309
609
909
C09
F09
00C
30C
60C
90C
C0C
F0C
*00F*
30F
60F
90F
C0F
*F0F*
030
330
630
930
C30
F30
033
333
633
933
C33
F33
036
336
636
936
C36
F36
039
339
639
939
C39
F39
03C
33C
63C
93C
C3C
F3C
03F
33F
63F
93F
C3F
F3F
060
360
660
960
C60
F60
063
363
663
963
C63
F63
066
366
666
966
C66
F66
069
369
669
969
C69
F69
06C
36C
66C
96C
C6C
F6C
06F
36F
66F
96F
C6F
F6F
090
390
690
990
C90
F90
093
393
693
993
C93
F93
096
396
696
996
C96
F96
099
399
699
999
C99
F99
09C
39C
69C
99C
C9C
F9C
09F
39F
69F
99F
C9F
F9F
0C0
3C0
6C0
9C0
CC0
FC0
0C3
3C3
6C3
9C3
CC3
FC3
0C6
3C6
6C6
9C6
CC6
FC6
0C9
3C9
6C9
9C9
CC9
FC9
0CC
3CC
6CC
9CC
CCC
FCC
0CF
3CF
6CF
9CF
CCF
FCF
*0F0*
3F0
*6F0*
9F0
CF0
*FF0*
0F3
*3F3*
*6F3*
9F3
CF3
*FF3*
*0F6*
*3F6*
6F6
9F6
*CF6*
*FF6*
0F9
3F9
6F9
9F9
CF9
FF9
*0FC*
*3FC*
6FC
9FC
CFC
FFC
*0FF*
*3FF*
*6FF*
9FF
CFF
*FFF*
Each color code listed is a shorthand for the RGB value. For example, code 609 is equivalent to RGB code 102-0-153 or HEX code #660099.
Safest web colors
Designers were encouraged[by whom?] 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 cyan.[30][31]
Safest web colors
R--
-GB
0
3
6
9
C
F
00
*000*
*F00*
03
*003*
*F03*
06
09
0C
0F
*00F*
*F0F*
⋮
⋮
F0
*0F0*
*6F0*
*FF0*
F3
*3F3*
*6F3*
*FF3*
F6
*0F6*
*3F6*
*CF6*
*FF6*
F9
FC
*0FC*
*3FC*
FF
*0FF*
*3FF*
*6FF*
*FFF*
Accessibility
Color selection
Some browsers 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.[32]
Color contrast
The Web Content Accessibility Guidelines recommend a contrast ratio of at least 4.5:1 between the relative luminance of text and its background color[33] 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 indicates,[34]dyslexic 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 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. The colors named in the report use different color values than the web colors of the same name.
Portable Network Graphics is a raster-graphics file format that supports lossless data compression. PNG was developed as an improved, non-patented replacement for Graphics Interchange Format (GIF)—unofficially, the initials PNG stood for the recursive acronym "PNG's not GIF".
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 additive primary colors, red, green, and blue.
RGBA stands for red green blue alpha. While it is sometimes described as a color space, it is actually a three-channel RGB color model supplemented with a fourth alpha channel. Alpha indicates how opaque each pixel is and allows an image to be combined over others using alpha compositing, with transparent areas and anti-aliasing of the edges of opaque regions.
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 <X11root>/lib/X11/rgb.txt. The web colors list is descended from it but differs for certain color names.
The various tones of the color coral are orange, red and pink representations of the colors of those cnidarians known as precious corals.
Lime is a color that is a shade of yellow-green, so named because it is a representation of the color of the citrus fruit called limes. It is the color that is in between the web color chartreuse and yellow on the color wheel. Alternate names for this color included yellow-green, lemon-lime, lime green, or bitter lime.
Aqua is a variation of the color cyan. The normalized color coordinates for the two web colors named aqua and cyan are identical. It was one of the three secondary colors of the RGB color model used on computer and television displays. In the HSV color wheel aqua is precisely halfway between blue and green. However, aqua is not the same as the primary subtractive color named process cyan used in printing.
Varieties of the color green may differ in hue, chroma or lightness, or in two or three of these qualities. Variations in value are also called tints and shades, a tint being a green or other hue mixed with white, a shade being mixed with black. A large selection of these various colors is shown below.
Varieties of the color red may differ in hue, chroma or lightness, or in two or three of these qualities. Variations in value are also called tints and shades, a tint being a red or other hue mixed with white, a shade being mixed with black. A large selection of these various colors are shown below.
In color science, a color gradient specifies a range of position-dependent colors, usually used to fill a region.
Web typography, like typography generally, is the design of pages – their layout and typeface choices. Unlike traditional print-based typography, pages intended for display on the World Wide Web have additional technical challenges and – given its ability to change the presentation dynamically – additional opportunities. Early web page designs were very simple due to technology limitations; modern designs use Cascading Style Sheets (CSS), JavaScript and other techniques to deliver the typographer's and the client's vision.
Animation of Scalable Vector Graphics, an open XML-based standard vector graphics format is possible through various means:
Cascading Style Sheets (CSS) is a style sheet language used for specifying the presentation and styling of a document written in a markup language such as HTML or XML. CSS is a cornerstone technology of the World Wide Web, alongside HTML and JavaScript.
In web development, the CSS box model refers to how HTML elements are modeled in browser engines and how the dimensions of those HTML elements are derived from CSS properties. It is a fundamental concept for the composition of HTML webpages. The guidelines of the box model are described by web standards World Wide Web Consortium (W3C) specifically the CSS Working Group. For much of the late-1990s and early 2000s there had been non-standard compliant implementations of the box model in mainstream browsers. With the advent of CSS2 in 1998, which introduced the box-sizing property, the problem had mostly been resolved.
Alice blue is a pale tint of azure that was favored by Alice Roosevelt Longworth, daughter of Theodore Roosevelt, which sparked a fashion sensation in the United States.
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.
This article provides introductory information about the RGB, HSV, and HSL color models from a computer graphics perspective. An introduction to colors is also provided to support the main discussion.
References
↑ Niederst Robbins, Jennifer (February 2006). "Appendix D: Specifying Color". Web Design in a Nutshell. O'Reilly. p.830. ISBN978-0-596-00987-8.
↑ Pemberton, Steven; Pettit, Brad (7 June 2011). Çelik, Tantek; Lilley, Chris; Baron, L. David (eds.). "4.2.1. RGB color values". CSS Color Module Level 3. W3C. Retrieved 19 March 2013.
↑ Pemberton, Steven; Pettit, Brad (7 June 2011). Çelik, Tantek; Lilley, Chris; Baron, L. David (eds.). "4.3. Extended color keywords". CSS Color Module Level 3. W3C. Retrieved 19 March 2013.
↑ Pemberton, Steven; Pettit, Brad (7 June 2011). Çelik, Tantek; Lilley, Chris; Baron, L. David (eds.). "4.5.1. CSS2 system colors". CSS Color Module Level 3. W3C. Retrieved 19 March 2013.
↑ Çelik, Tantek, ed. (17 January 2012). "List of substantial changes". CSS Basic User Interface Module Level 3. W3C. Retrieved 19 March 2013. System Appearance has been dropped, including appearance values & property, and system fonts / extension of the 'font' property shorthand.
1 2 Pemberton, Steven; Pettit, Brad (7 June 2011). Çelik, Tantek; Lilley, Chris; Baron, L. David (eds.). "4.2.4. HSL color values". CSS Color Module Level 3. W3C. Retrieved 19 March 2013.
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