Hexadecimal
The hexadecimal (hex) system is a general term describing a numerical system with
base 16. In it, the numbers zero to nine are paired with the letters A through F to pro‑
vide 16 total characters. Hex is used for many purposes other than color coding, but
if your work involves displaying maps on the Web via HTML, you will need a good
understanding of hex color system, which is a derivative of the RGB color model.
Whereas the RGB colors are specified by means of three numbers, the hex system
uses three pairs of letters and numbers. Hex is specifically used for hard‑coding
colors for display on a monitor