For anyone wondering, hex color is just in base 16. So 255 (max color) is FF.
The 6 long string of characters is just the Red Green and Blue channels (RRGGBB).
Which means you shouldn't have to look it up unless you're going for an exact color.
Hex numbers: 0 1 2 3 4 5 6 7 8 9 A B C D E F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21.. etc.