Feral Heart

I've been trying to make a 6 color mask for this mapped group i've got and i think i know how to make one but it keeps stuffing up.. I made one mask with the RGB (Red, Green, Blue) and then add black to palces, next a do a new one adn color in the places that were RGB in black and the black in my new colors (I doing this all in GIMP i cna only use GIMP x.x) That works fine and it loads into the game fine, but when i add the colors RGB Work fine, but the other one i made dose not the first colors works and then the other two color over all 3 of them... Could some one help me out with this? soon Please  (Sorry for any spelling errors i may have)