http://b3aelitqz4izuqd7gqhol6s5jdi7bh3vrvws2sifypdgucfzbiizhrad.onion/app.php/help/bbcode
You can specify either a recognised colour name (eg. red, blue, yellow, etc.) or the hexadecimal triplet alternative, e.g. #FFFFFF, #000000. For example, to create red text you could use: [color=red] Hello! [/color] or [color=#FF0000] Hello! [/color] Both will output Hello!