I often start by putting a simple gradient in the background. I'm feeling an evil version of Yori would like be into deep lavender. Don't question my artistic vision!! First I select to shades of purple I like, and then I select my gradient tool.

I then go about adding my my gradient to my background layer. Now, when I start adding base colors, I'll be aware if they look a little un-unified. Normally you might want to make your character's skin a fleshy yellowish-pink, and a character's clothing green or what not. But with a nice color like purple sitting in the background, you'll unconciously keep your colors a little more purple than if your background was white.

If that's too hard to follow, hopefully it'll make more sense as we go along.

Select your base colors layer. This is the part where you get to live out your grade school fantasies of coloring in the lines in coloring books. Choose a base color for your character's hair, skin, clothing, and any items he/she/it might have. try not to make them too jarring against that background gradient. Something else important to keep in mind is that these colors are going to be your light colors, as in where the light will be hitting. If you have a black color, like Yori's hair, make it a dark red, purple, or blue. few things are completely black when light hits them.

Stay in the lines, also! If a little bit of skin color shoots out past your character's nose, it's going to look mighty odd, so just make sure to fix such imperfections with the eraser tool. You also don't have to do all the base colors on one layer, but if you do them on seperate layers, you will have to merge them together once you're finished.

Make certain you're coloring on the base color layer! you're going to be wanting to duplicate this layer once you're done, so if you color all the base colors onto the gradient or linework layer, no can do. Well, I guess you could just duplicate that layer, but then you'll be duplicating the linework or gradient as well, which might be interesting, but it won't help with this coloring method.