And Maldret sorry but I can't give you any tips on how to color it, because I don't have a tablet therefor I don't have experience. If I where you I would simply paint it in black and white, giving it shades.
Basically my opinion is the same has Will's. Finish it first and make the mapping better, then you can start coloring it (: you could browse DeviantArt to have some inspiration and see how other people do it, because I can't really give you a lesson xD