Its all very simple, [@Rilla].

They go from 00 to FF, with the first two being [color=ff0000]red[/color], second two being [color=00ff00]green[/color], third two being [color=0000ff]blue[/color]. the higher the value, the more of that color component is included. Unless you're really focused, you don't bother to memorize exactly what values make up a certain "named" color, you simply use what is roughly around it, perhaps experimenting with preview to confirm it is what you want.