Web colors
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.
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.
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.
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 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.
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.
"[9] Extended colors are the result of merging specifications from HTML 4.01, CSS 2.0, SVG 1.0 and CSS3 User Interfaces (CSS3 UI).
The list of colors shipped with the X11 product varies between implementations and clashes with certain of the HTML names such as green.
[10] The list of web "X11 colors" from the CSS3 specification, along with their hexadecimal and decimal equivalents, is shown below.
This enables web authors to style their content in line with the operating system of the user agent.
[22] The CSS3 specification also introduces HSL color space values to style sheets:[23] 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).
Some sections explaining color theory and common operations like gamut mapping are also added to aid implementation.
[24] 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.
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).
These colors were chosen specifically because they matched the palettes selected by various browser applications.
Values flanked by "*" (asterisk) are part of the "really safe palette;" see Safest web colors, below.
They called these 22 colors "the really safe palette"; it consists largely of shades of green, yellow, and cyan.
For these displays or blind and colorblind users, Web content depending on colors can be unusable or difficult to use.
As a report to the Web Accessibility Initiative indicates,[34] dyslexic readers are better served by contrast ratios below the maximum.
