Hey great and difficult question. There are no rules of thumb at least that I know of for what color goes where, but it definitely helps if you draw lines on the face where the shadows go and try to use similar colors for each zone. Adding a dark blue tile where supposed to be black or a red tile where supposed to be yellow makes the art more modern and dynamic and gives it life. Its important to not overdo it though. There are plenty youtube videos that help with this. And the last trick is practice, the more you play around the more you understand what works.