I used to think about making this tutorial before December. But then i took Skyrim to the knee.
Anyway, this is how i do my work lately. coloring will be much easier by using texture (actually , its more like texture + light + shadow). pretty useful for works that you want to roughly determine lighting and texture before coloring it.
This tutorial work with most layer-based graphic application. (Photoshop , Corel Painter , SAI , Open Canvas)