HTML and CSS Reference
This is a hex-pair notation familiar to authors using traditional HTML. In this format, the
first pair of digits corresponds to the red level, the second pair to the green, and the third
pair to the blue. Each pair is in hexadecimal notation in the range 00 - FF . Thus, a “pure”
blue is written #0000FF , a “pure” red is written #FF0000 , and so on.
This is a shorter form of the six-digit notation described previously. In this format, each
digit is replicated to arrive at an equivalent six-digit value; thus, #F8C becomes #FF88CC .
This format allows the author to use RGB values in the range 0 - 255 ; only integers are
permitted. Not coincidentally, this range is the decimal equivalent of 00 - FF in hexadecim-
al. In this format, “pure” green is rgb (0,255,0) , and white is represented as rgb
This format allows the author to use RGB values in the range 0% to 100% , with decimal
values allowed (e.g., 75.5% ). The value for black is thus rgb (0%,0%,0%) , whereas “pure”
blue is rgb (0%,0%,100%) .
This format permits authors to specify a color by its hue angle, saturation, and lightness
(thus HSL). The hue angle is always a unitless number in the range 0 to 360 and the satur-
ation and brightness values are always percentages. Hue angles 0 and 360 are equivalent,
and are both red. Hue angles greater than 360 can be declared but they are normalized to
the 0-360 range; thus, setting a hue angle of 454 is equivalent to setting an angle of 94 .
Any HSL value, regardless of color angle, will be rendered as a shade of gray if the sat-
uration value is 0% ; the exact shade will depend on the lightness value. Any HSL value,
regardless of the hue angle, will be rendered solid black if lightness is 0% and solid white
if lightness is 100% . The “normal” lightness value—that is, the value associated with most
common colors—is 50% .