Color
The arithmetic of colours
Colour Wheel
H (hue) is an angle (degrees by default if no units are given). Red is 0 or 360, green 120, and blue 240.
S (saturation) ranges from 100% for fully the hue to 0% for gray.
L (lightness) is 50% for “normal”. 100% is black and 0% is white.
A (alpha) can be a number between 0 and 1, or a percentage, where the number 1 corresponds to 100% (full opacity).