10) Using the PENCIL tool, select the colors you desire for the BODY, LEGS/MUZZLE, EYES and fill in the areas roughly. The layers neatly preserves your original black lines. Huzzah!
11) Now, select a color slightly darker than your original colors (for each color) and fill in your shadowed areas.
Highlights add depth to the picture in combination with the shadows. Remember, however, that light can come from multiple directions, but simplicity in poses usually has light coming from one place. the left, right, top, side, etc. I tend to make my light cast down from the top.
Once you are at this stage, you can start using the air brush to do more subtle details. Beware the over use of the SMUDGE tool, as seen on a lot of poses for people who are too lazy to shade.
12) When forced to use a mouse to airbrush, I set it at 17% opacity. Tablet users have no such need and have leave the setting at 100% and let their own hand pressure guide the opacity. After using the airbrush and other tools of your preference to bring the pose up to standard, it should look something like this
The poses to the rightwas colored with a mouse. You can use the BLUR tool (it looks like a water drop on the toolbar) to smooth the borders between your colors. It's is better to use the BLUR tool before you use the SMUDGE tool! The Smudge tool makes a mess more often than not in the hands of someone who cannot control themselves.
The pose to the right was colored on a tablet, which allows for a bit more hand control for repeating strokes. The methods are the same, regardless of using mouse or tablet stylus.