Sorry for the slow reply. I'm not entirely sure what your question is, but here goes. Especially when you are doing fanart, where all of the colors are already decided before you even go to work, the base colors can be kind of dull. Obviously, when you are doing original work, choosing your blend of which color goes where is much more engaging. But in either case, shading is your domain.



Now there are two parts to shading at a basic level: shadows and highlights. I've seen many artists start at the midtones and do lots of shading and lots of highlights, but I have a (perhaps negative) tendency to start towards the brighter side and shade down. A common misconception is that shadows are just darker hues of the surface they are reflected on. Maybe they are, but there's no feeling to turning something darker. Unfortunately, I couldn't find the clip, but if you go watch "Vincent and the Doctor"(Dr. Who 05-10), Vincent gives a good explanation of subtle colors towards the end of the episode.



What color you shadows are, and what color your highlights are set a mood for the piece as a whole. Reds are more energetic, more aggressive, while blues are more mellow. Be careful, as I've found blues to sap too much energy from the drawing unless used right, and greens can give a sickly appearance. There are thousands of colors, so each one will give a certain impact. The trick is just finding which one you need. Of course, some things, like candle light, are a given color, and you have to act with that as a given. But in such a situation, you should instead think about how the candle fits into the piece as a whole.



I should point out that a lot of it is balance, which i can't help you with near as much as I would like to. I hope this answers your question.