Web colors

Web colors are colors used in displaying web pages on the World Wide Web, and the methods for describing and specifying those colors. Colors may be specified as an RGB triplet or in hexadecimal format (a hex triplet) or according to their common English names 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, in order 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, three-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. 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.[5] Expanding this form to the six-digit form is as simple as doubling 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

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 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

The HTML 4.01 specification, ratified in 1999, defines 16 named colors,[6] 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."[7]

X11 color names

A number of 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.[8]

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 (common sRGB name) and fuchsia (HTML4/CSS 1.0 standard name), gray (HTML4/CSS 1.0 standard name) and grey.[9][10]

HTML name R   G   B
Hex Decimal
Pink colors
PinkFF C0 CB255 192 203
LightPinkFF B6 C1255 182 193
HotPinkFF 69 B4255 105 180
DeepPinkFF 14 93255  20 147
PaleVioletRedDB 70 93219 112 147
MediumVioletRedC7 15 85199  21 133
Red colors
LightSalmonFF A0 7A255 160 122
SalmonFA 80 72250 128 114
DarkSalmonE9 96 7A233 150 122
LightCoralF0 80 80240 128 128
IndianRedCD 5C 5C205  92  92
CrimsonDC 14 3C220  20  60
FirebrickB2 22 22178  34  34
DarkRed8B 00 00139   0   0
RedFF 00 00255   0   0
Orange colors
OrangeRedFF 45 00255  69   0
TomatoFF 63 47255  99  71
CoralFF 7F 50255 127  80
DarkOrangeFF 8C 00255 140   0
OrangeFF A5 00255 165   0
Yellow colors
YellowFF FF 00255 255   0
LightYellowFF FF E0255 255 224
LemonChiffonFF FA CD255 250 205
LightGoldenrodYellow FA FA D2250 250 210
PapayaWhipFF EF D5255 239 213
MoccasinFF E4 B5255 228 181
PeachPuffFF DA B9255 218 185
PaleGoldenrodEE E8 AA238 232 170
KhakiF0 E6 8C240 230 140
DarkKhakiBD B7 6B189 183 107
GoldFF D7 00255 215   0
Brown colors
CornsilkFF F8 DC255 248 220
BlanchedAlmondFF EB CD255 235 205
BisqueFF E4 C4255 228 196
NavajoWhiteFF DE AD255 222 173
WheatF5 DE B3245 222 179
BurlywoodDE B8 87222 184 135
TanD2 B4 8C210 180 140
RosyBrownBC 8F 8F188 143 143
SandyBrownF4 A4 60244 164  96
GoldenrodDA A5 20218 165  32
DarkGoldenrodB8 86 0B184 134  11
PeruCD 85 3F205 133  63
ChocolateD2 69 1E210 105  30
SaddleBrown8B 45 13139  69  19
SiennaA0 52 2D160  82  45
BrownA5 2A 2A165  42  42
Maroon80 00 00128   0   0
HTML name R   G   B
Hex Decimal
Green colors
DarkOliveGreen55 6B 2F 85 107  47
Olive80 80 00128 128   0
OliveDrab6B 8E 23107 142  35
YellowGreen9A CD 32154 205  50
LimeGreen32 CD 32 50 205  50
Lime00 FF 00  0 255   0
LawnGreen7C FC 00124 252   0
Chartreuse7F FF 00127 255   0
GreenYellowAD FF 2F173 255  47
SpringGreen00 FF 7F  0 255 127
MediumSpringGreen 00 FA 9A  0 250 154
LightGreen90 EE 90144 238 144
PaleGreen98 FB 98152 251 152
DarkSeaGreen8F BC 8F143 188 143
MediumAquamarine66 CD AA102 205 170
MediumSeaGreen3C B3 71 60 179 113
SeaGreen2E 8B 57 46 139  87
ForestGreen22 8B 22 34 139  34
Green00 80 00  0 128   0
DarkGreen00 64 00  0 100   0
Cyan colors
Aqua00 FF FF  0 255 255
Cyan00 FF FF  0 255 255
LightCyanE0 FF FF224 255 255
PaleTurquoiseAF EE EE175 238 238
Aquamarine7F FF D4127 255 212
Turquoise40 E0 D0 64 224 208
MediumTurquoise48 D1 CC 72 209 204
DarkTurquoise00 CE D1  0 206 209
LightSeaGreen20 B2 AA 32 178 170
CadetBlue5F 9E A0 95 158 160
DarkCyan00 8B 8B  0 139 139
Teal00 80 80  0 128 128
Blue colors
LightSteelBlueB0 C4 DE176 196 222
PowderBlueB0 E0 E6176 224 230
LightBlueAD D8 E6173 216 230
SkyBlue87 CE EB135 206 235
LightSkyBlue87 CE FA135 206 250
DeepSkyBlue00 BF FF  0 191 255
DodgerBlue1E 90 FF 30 144 255
CornflowerBlue64 95 ED100 149 237
SteelBlue46 82 B4 70 130 180
RoyalBlue41 69 E1 65 105 225
Blue00 00 FF  0   0 255
MediumBlue00 00 CD  0   0 205
DarkBlue00 00 8B  0   0 139
Navy00 00 80  0   0 128
MidnightBlue19 19 70 25  25 112
HTML name R   G   B
Hex Decimal
Purple, violet, and magenta colors
LavenderE6 E6 FA230 230 250
ThistleD8 BF D8216 191 216
PlumDD A0 DD221 160 221
VioletEE 82 EE238 130 238
OrchidDA 70 D6218 112 214
FuchsiaFF 00 FF255   0 255
MagentaFF 00 FF255   0 255
MediumOrchidBA 55 D3186  85 211
MediumPurple93 70 DB147 112 219
BlueViolet8A 2B E2138  43 226
DarkViolet94 00 D3148   0 211
DarkOrchid99 32 CC153  50 204
DarkMagenta8B 00 8B139   0 139
Purple80 00 80128   0 128
Indigo4B 00 82 75   0 130
DarkSlateBlue48 3D 8B 72  61 139
SlateBlue6A 5A CD106  90 205
MediumSlateBlue 7B 68 EE123 104 238
White colors
WhiteFF FF FF255 255 255
SnowFF FA FA255 250 250
HoneydewF0 FF F0240 255 240
MintCreamF5 FF FA245 255 250
AzureF0 FF FF240 255 255
AliceBlueF0 F8 FF240 248 255
GhostWhiteF8 F8 FF248 248 255
WhiteSmokeF5 F5 F5245 245 245
SeashellFF F5 EE255 245 238
BeigeF5 F5 DC245 245 220
OldLaceFD F5 E6253 245 230
FloralWhiteFF FA F0255 250 240
IvoryFF FF F0255 255 240
AntiqueWhiteFA EB D7250 235 215
LinenFA F0 E6250 240 230
LavenderBlushFF F0 F5255 240 245
MistyRoseFF E4 E1255 228 225
Gray and black colors
GainsboroDC DC DC220 220 220
LightGrayD3 D3 D3211 211 211
SilverC0 C0 C0192 192 192
DarkGrayA9 A9 A9169 169 169
Gray80 80 80128 128 128
DimGray69 69 69105 105 105
LightSlateGray77 88 99119 136 153
SlateGray70 80 90112 128 144
DarkSlateGray2F 4F 4F 47  79  79
Black00 00 00  0   0   0

Web-safe colors

In the mid-90s, many displays were only capable of displaying 256 colors.[11] 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 one available, a different one had to be used. This can be 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 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 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.

As of 2011, personal computers typically[12] have 24-bit (TrueColor) 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 or (12) CC 204 0.8
F or (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.

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 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 reallysafe palette"; it consists largely of shades of green, yellow, and blue, as can be seen in the table below.[13]

Safest web colors
0 3 6 9 C F
00 *000* *F00*
03 *003* *F03*
0F *00F* *F0F*
F0 *0F0* *6F0* *FF0*
F3 *3F3* *6F3* *FF3*
F6 *0F6* *3F6* *CF6* *FF6*[14]
FC *0FC* *3FC*
FF *0FF* *3FF* *6FF* *FFF*

CSS colors

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.[15] 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.[16]

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.[17] The CSS3.0 specification did not include orange in the "HTML4 color keywords" section, which was renamed as "Basic color keywords".[18] 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.[19] The working draft for the CSS4 color module combines the Basic and Extended sections together in a simple "Named Colors" section.[20]

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.[21] The CSS3 color module has deprecated the use of system colors in favor of CSS3 UI System Appearance property,[22][23] which itself was subsequently dropped from CSS3.[24]

The developing CSS3 specification also introduces HSL color space values to style sheets:[25]

 /* 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 */

On 21 June 2014, the CSS WG added the color RebeccaPurple to the Editor's Draft of the CSS4 Colors module, 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%

Accessibility

Color selection

Some browsers and devices do not support colors. For these displays, or for 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.[27]

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[28] 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,[29] dyslexic readers are better served by contrast ratios below the maximum. The recommendations they refer to of off-black (0x0A0A0A) on off-white (0xFFFFE5) and black (0x000000) on creme (0xFAFAC8) have contrast ratios of 11.7:1 and 20.3:1 respectively. Among their other color pairs, brown (0x282800) on dark green (0xA0A000) has a contrast ratio of 3.24:1, which is less than the WCAG recommendation, dark brown (0x1E1E00) on light green (0xB9B900) has a contrast ratio of 4.54:1 and blue (0x00007D) on yellow (0xFFFF00) 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

  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. Digital Color Imaging Handbook By Gaurav Sharma. ISBN 0-8493-0900-X
  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. "HTML 4.01 Specification section 6.5 "Colors"". W3.org. Retrieved 8 July 2013.
  7. "HTML 3.2 Specification "The BODY element"". W3.org. Retrieved 8 July 2013.
  8. "Public discussion on SVG mailing list Re: color names in SVG-1.0 conflict with /usr/lib/X11/rgb.txt". Lists.w3.org. Retrieved 8 July 2013.
  9. 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.
  10. "W3C TR SVG 1.0, recognized color keyword names". W3.org. 16 August 2011. Retrieved 1 February 2019.
  11. Jenkins, Sue (27 December 2012). Web Design All-in-One For Dummies. John Wiley & Sons. ISBN 9781118404119.
  12. "Browser Display Statistics". W3schools.com. Retrieved 8 July 2013.
  13. "Death of the Websafe Color Palette?". Physics.ohio-state.edu. Retrieved 8 July 2013.
  14. "Web Color Reference - HTML with Style | 4 | WebReference". www.webreference.com. Retrieved 5 January 2016.
  15. "The X11 Color Set". Retrieved 6 July 2014.
  16. Brian Wilson. "Colors in HTML and CSS". Retrieved 6 July 2014.
  17. "CSS 2.1 Specification: Syntax and basic data types: Colors". 8 September 2009. Retrieved 21 December 2009.
  18. "CSS Color Module Level 3 – Proposed Recommendation - 11. Changes". 28 October 2010. Retrieved 6 July 2014.
  19. "CSS Color Module Level 3 – Working Draft". 18 April 2002. Retrieved 6 July 2014.
  20. CSS Color Module Level 4  Editor’s Draft, 26 June 2014
  21. "User interface – System colors". W3.org. Retrieved 8 July 2013.
  22. 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.
  23. "CSS3 Basic User Interface Module, W3C Candidate Recommendation 11 May 2004: System Appearance". W3.org. Retrieved 8 July 2013.
  24. 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.
  25. 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.
  26. Glazman, Daniel (21 June 2014). "Re: [CfC] adding 'rebeccapurple' to CSS Color Level 4". Post to www-style mailing list. W3C. Retrieved 24 June 2014.
  27. "If You Pick One Color, Pick Them All". W3.org. Retrieved 8 July 2013.
  28. WCAG 2.0 guideline 1.4
  29. Optimal Colors to Improve Readability for People with Dyslexia
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