Color is in the format RRGGBBAA, where AA denotes the opacity of the alpha channel. You can look at it as the opacity of the the color chosen. Except, with white/grey/black it works differently, and I haven't quite figured out how.
Also, the menu.ini renumberer referenced above is a product of h.sie. You can find his mod page under his sig in the Realism- and gameplay-related hardcode fixes for SH3.EXE thread stickied at the top of the mods forum.
Good luck!
