HTML Colour codes let you post 256 shades of red, green and blue to make one of over 16.7 MILLION colours.
A Colour code is usually used in HTML using the structure "#rrggbb", and it encapsulates the 2-digit HEXADECIMAL amounts (0..255/00..ff) of each of the 3 primaries. HTML also misspells colour as COLOR (*shakes fist at the Americas).
NOTE: Just because a colour EXISTS, it does not mean you have to USE it or that your browser will faithfullr render it #justsayin'
Dial amounts of each colour above then submit to display