Well the thing about color is that there are so many factors to consider. Not when you just paint a character on white canvas, but especially when you try to place that character in an environment. First, that environment needs to have an interesting color setting, which is most apparent when looking at a thumbnail. Daarken's pictures comes to mind. Then, that character has to blend with the surroundings, like it actually belongs in that enviroment and doesnt awkwardly pop out.
The first apparent question to answer before painting in color is: Do I start from greyscale? Or do I go straight into color? See, when start in greyscale, I have a hard time coloring it with color layers. Colors just lie there like ugly blobs so obviously made with a soft round brush. (I'm talking Photoshop) Then, if I go straight with color, I just don't know how to handle them, how not to use too saturated colors, how to color shadows in a way that actually makes sense in that particular environment so everything has the correct hue, saturation and brigtness. I suppose greyscale is the way to go, that way the brigthness is already established. I just don't understand yet, how to color a greyscale image so that it doesn't mess up the values that were already established. Another knowledge I have yet to acquire is how to tweak the colors with adjustment layers to make an interesting color setting.