A number system with a base of 16. 0-9 and A-F are used to represent the digits.
The format is #rrggbb, where rr, gg, and bb are two-digit hexadecimal values for the red, green, and blue components of the color. 00 is the minimum value and FF is the maximum, 88 is the median.
For example, the color white is #FFFFFF, the color black is #000000, the color red is #FF0000, the color green is #00FF00, and the color blue is #0000FF.