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Web colors

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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

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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=123, green=58, blue=30 (a hardwood brown color). The decimal numbers 123, 58, and 30 are equivalent to the hexadecimal numbers 7B, 3A, and 1E, respectively. The hex triplet is obtained by concatenating the six hexadecimal digits together, 7B3A1E 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 2563, 166, or 224 = 16,777,216.

Shorthand hexadecimal form

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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.

Converting RGB to hexadecimal

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See also: Hexadecimal § Conversion

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 (as shown in the previous example of hex triplets) 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

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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

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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):

CSS 1–2.0, HTML 3.2–4, and VGA color names
Name Hex
(RGB) 		Red
(RGB) 		Green
(RGB) 		Blue
(RGB) 		Hue
(HSL/HSV) 		Satur.
(HSL) 		Light
(HSL) 		Satur.
(HSV) 		Value
(HSV)		 CGA number (name); alias
White #FFFFFF 100% 100% 100% 0° 0% 100% 0% 100% 15 (white)
Silver #C0C0C0 75% 75% 75% 0° 0% 75% 0% 75% 07 (light gray)
Gray #808080 50% 50% 50% 0° 0% 50% 0% 50% 08 (dark gray)
Black #000000 0% 0% 0% 0° 0% 0% 0% 0% 00 (black)
Red #FF0000 100% 0% 0% 0° 100% 50% 100% 100% 12 (high red)
Maroon #800000 50% 0% 0% 0° 100% 25% 100% 50% 04 (low red)
Yellow #FFFF00 100% 100% 0% 60° 100% 50% 100% 100% 14 (yellow)
Olive #808000 50% 50% 0% 60° 100% 25% 100% 50% 06 (brown)
Lime #00FF00 0% 100% 0% 120° 100% 50% 100% 100% 10 (high green); green
Green #008000 0% 50% 0% 120° 100% 25% 100% 50% 02 (low green)
Aqua #00FFFF 0% 100% 100% 180° 100% 50% 100% 100% 11 (high cyan); cyan
Teal #008080 0% 50% 50% 180° 100% 25% 100% 50% 03 (low cyan)
Blue #0000FF 0% 0% 100% 240° 100% 50% 100% 100% 09 (high blue)
Navy #000080 0% 0% 50% 240° 100% 25% 100% 50% 01 (low blue)
Fuchsia #FF00FF 100% 0% 100% 300° 100% 50% 100% 100% 13 (high magenta); magenta
Purple #800080 50% 0% 50% 300° 100% 25% 100% 50% 05 (low magenta)

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

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SVG Version of X11 color names
SVG1.1 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]

HTML name R G B
Hex Decimal
Pink colors
MediumVioletRed C71585 199, 21, 133
DeepPink FF1493 255, 20, 147
PaleVioletRed DB7093 219, 112, 147
HotPink FF69B4 255, 105, 180
LightPink FFB6C1 255, 182, 193
Pink FFC0CB 255, 192, 203
Red colors
DarkRed 8B0000 139, 0, 0
Red FF0000 255, 0, 0
Firebrick B22222 178, 34, 34
Crimson DC143C 220, 20, 60
IndianRed CD5C5C 205, 92, 92
LightCoral F08080 240, 128, 128
Salmon FA8072 250, 128, 114
DarkSalmon E9967A 233, 150, 122
LightSalmon FFA07A 255, 160, 122
Orange colors
OrangeRed FF4500 255, 69, 0
Tomato FF6347 255, 99, 71
DarkOrange FF8C00 255, 140, 0
Coral FF7F50 255, 127, 80
Orange FFA500 255, 165, 0
Yellow colors
DarkKhaki BDB76B 189, 183, 107
Gold FFD700 255, 215, 0
Khaki F0E68C 240, 230, 140
PeachPuff FFDAB9 255, 218, 185
Yellow FFFF00 255, 255, 0
PaleGoldenrod EEE8AA 238, 232, 170
Moccasin FFE4B5 255, 228, 181
PapayaWhip FFEFD5 255, 239, 213
LightGoldenrodYellow FAFAD2 250, 250, 210
LemonChiffon FFFACD 255, 250, 205
LightYellow FFFFE0 255, 255, 224
Brown colors
Maroon 800000 128, 0, 0
Brown A52A2A 165, 42, 42
SaddleBrown 8B4513 139, 69, 19
Sienna A0522D 160, 82, 45
Chocolate D2691E 210, 105, 30
DarkGoldenrod B8860B 184, 134, 11
Peru CD853F 205, 133, 63
RosyBrown BC8F8F 188, 143, 143
Goldenrod DAA520 218, 165, 32
SandyBrown F4A460 244, 164, 96
Tan D2B48C 210, 180, 140
Burlywood DEB887 222, 184, 135
Wheat F5DEB3 245, 222, 179
NavajoWhite FFDEAD 255, 222, 173
Bisque FFE4C4 255, 228, 196
BlanchedAlmond FFEBCD 255, 235, 205
Cornsilk FFF8DC 255, 248, 220
HTML name R G B
Hex Decimal
Purple, violet, and magenta colors
Indigo 4B0082 75, 0, 130
Purple 800080 128, 0, 128
DarkMagenta 8B008B 139, 0, 139
DarkViolet 9400D3 148, 0, 211
DarkSlateBlue 483D8B 72, 61, 139
BlueViolet 8A2BE2 138, 43, 226
DarkOrchid 9932CC 153, 50, 204
Fuchsia FF00FF 255, 0, 255
Magenta FF00FF 255, 0, 255
SlateBlue 6A5ACD 106, 90, 205
MediumSlateBlue 7B68EE 123, 104, 238
MediumOrchid BA55D3 186, 85, 211
MediumPurple 9370DB 147, 112, 219
Orchid DA70D6 218, 112, 214
Violet EE82EE 238, 130, 238
Plum DDA0DD 221, 160, 221
Thistle D8BFD8 216, 191, 216
Lavender E6E6FA 230, 230, 250
Blue colors
MidnightBlue 191970 25, 25, 112
Navy 000080 0, 0, 128
DarkBlue 00008B 0, 0, 139
MediumBlue 0000CD 0, 0, 205
Blue 0000FF 0, 0, 255
RoyalBlue 4169E1 65, 105, 225
SteelBlue 4682B4 70, 130, 180
DodgerBlue 1E90FF 30, 144, 255
DeepSkyBlue 00BFFF 0, 191, 255
CornflowerBlue 6495ED 100, 149, 237
SkyBlue 87CEEB 135, 206, 235
LightSkyBlue 87CEFA 135, 206, 250
LightSteelBlue B0C4DE 176, 196, 222
LightBlue ADD8E6 173, 216, 230
PowderBlue B0E0E6 176, 224, 230
Cyan colors
Teal 008080 0, 128, 128
DarkCyan 008B8B 0, 139, 139
LightSeaGreen 20B2AA 32, 178, 170
CadetBlue 5F9EA0 95, 158, 160
DarkTurquoise 00CED1 0, 206, 209
MediumTurquoise 48D1CC 72, 209, 204
Turquoise 40E0D0 64, 224, 208
Aqua 00FFFF 0, 255, 255
Cyan 00FFFF 0, 255, 255
Aquamarine 7FFFD4 127, 255, 212
PaleTurquoise AFEEEE 175, 238, 238
LightCyan E0FFFF 224, 255, 255
HTML name R G B
Hex Decimal
Green colors
DarkGreen 006400 0, 100, 0
Green 008000 0, 128, 0
DarkOliveGreen 556B2F 85, 107, 47
ForestGreen 228B22 34, 139, 34
SeaGreen 2E8B57 46, 139, 87
Olive 808000 128, 128, 0
OliveDrab 6B8E23 107, 142, 35
MediumSeaGreen 3CB371 60, 179, 113
LimeGreen 32CD32 50, 205, 50
Lime 00FF00 0, 255, 0
SpringGreen 00FF7F 0, 255, 127
MediumSpringGreen 00FA9A 0, 250, 154
DarkSeaGreen 8FBC8F 143, 188, 143
MediumAquamarine 66CDAA 102, 205, 170
YellowGreen 9ACD32 154, 205, 50
LawnGreen 7CFC00 124, 252, 0
Chartreuse 7FFF00 127, 255, 0
LightGreen 90EE90 144, 238, 144
GreenYellow ADFF2F 173, 255, 47
PaleGreen 98FB98 152, 251, 152
White colors
MistyRose FFE4E1 255, 228, 225
AntiqueWhite FAEBD7 250, 235, 215
Linen FAF0E6 250, 240, 230
Beige F5F5DC 245, 245, 220
WhiteSmoke F5F5F5 245, 245, 245
LavenderBlush FFF0F5 255, 240, 245
OldLace FDF5E6 253, 245, 230
AliceBlue F0F8FF 240, 248, 255
Seashell FFF5EE 255, 245, 238
GhostWhite F8F8FF 248, 248, 255
Honeydew F0FFF0 240, 255, 240
FloralWhite FFFAF0 255, 250, 240
Azure F0FFFF 240, 255, 255
MintCream F5FFFA 245, 255, 250
Snow FFFAFA 255, 250, 250
Ivory FFFFF0 255, 255, 240
White FFFFFF 255, 255, 255
Gray and black colors
Black 000000 0, 0, 0
DarkSlateGray 2F4F4F 47, 79, 79
DimGray 696969 105, 105, 105
SlateGray 708090 112, 128, 144
Gray 808080 128, 128, 128
LightSlateGray 778899 119, 136, 153
DarkGray A9A9A9 169, 169, 169
Silver C0C0C0 192, 192, 192
LightGray D3D3D3 211, 211, 211
Gainsboro DCDCDC 220, 220, 220

CSS colors

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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]

Color added in CSS 2.1
Name Hex
(RGB) 		Red
(RGB) 		Green
(RGB) 		Blue
(RGB) 		Hue
(HSL/HSV) 		Satur.
(HSL) 		Light
(HSL) 		Satur.
(HSV) 		Value
(HSV)		 Alias
Orange #FFA500 100% 65% 0% 39° 100% 50% 100% 100%

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

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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

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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]

Predefined color spaces

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A number of RGB spaces with gamuts that are wider than sRGB are also introduced through the new color() function:[25]

A linearized variant of sRGB is also defined for color mixing.[24]

Other formats

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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]

Color added in CSS4 Colors module
Name Hex
(RGB) 		Red
(RGB) 		Green
(RGB) 		Blue
(RGB) 		Hue
(HSL/HSV) 		Satur.
(HSL) 		Light
(HSL) 		Satur.
(HSV) 		Value
(HSV)		 Alias
RebeccaPurple #663399 40% 20% 60% 270° 50% 40% 67% 60%

CSS4 also introduces the HWB color model as an alternative to HSL/HSV.[18]

CSS Color 5

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The draft CSS Color 5[27] 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 profiles. This allows the use of CMYK on web pages.[27]

Web-safe colors

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Color depth
Related

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

[edit]
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

[edit]

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

[edit]

Color selection

[edit]

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

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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.

See also

[edit]

References

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  1. ^ Niederst Robbins, Jennifer (February 2006). "Appendix D: Specifying Color". Web Design in a Nutshell. O'Reilly. p. 830. ISBN 978-0-596-00987-8.
  2. ^ York, Richard. Beginning CSS, pp. 71–72.
  3. ^ Pemberton, Steven; Pettit, Brad (7 June 2011). Çelik, Tantek; Lilley, Chris; Baron, L. David (eds.). "CSS Color Module Level 3". W3C. section 4.2.1. RGB color values.
  4. ^ Sharma, Gaurav; Bala, Raja (19 December 2017). Digital Color Imaging Handbook. CRC Press. ISBN 978-1-4200-4148-4.
  5. ^ 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.
  6. ^ a b "CSS Color Module Level 3". W3c. Retrieved 19 July 2020.
  7. ^ Powell, Thomas A. (2010). HTML & CSS: The Complete Reference, Fifth Edition. New York: McGraw-Hill. p. 765. ISBN 9780071741705.
  8. ^ "HTML 4.01 Specification | Basic HTML data types | Colors". W3C. Retrieved 8 July 2013.
  9. ^ Raggett, Dave. "HTML 3.2 Reference Specification | The BODY element". W3C. Retrieved 8 July 2013.
  10. ^ Lilley, Chris (24 April 2002). "Re: color names in SVG-1.0 conflict with /usr/lib/X11/rgb.txt". W3C Public mailing list archives. Retrieved 8 July 2013.
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  33. ^ WCAG 2.0 guideline 1.4
  34. ^ Optimal Colors to Improve Readability for People with Dyslexia
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