There are a few ways to color nice crisp character in the Flash Tool
First, Use the Guide layer to Sketch out what you want, Then trace over it with the skinny straight line tool. (for crisp edges) You can to this in any light color. 100% opacity.
Next, Create a background. It is a lot easier to do this first, than having to trace tediously around your subject.
Third, using a wider thickness, trace your figure with the color you want it to be. 100% Opacity.
Carefully fill in your figure. I found it easier to control a wide Line Tool when doing this. Think of it as a wide marker that only goes in straight lines. xD
Using the Guide layer to... well.. Guide you, fill in the details. I used the same technique used on the body for the hair. I used a 30% opacity darker flesh color to add these details using the Fill Tool and Line tool.
Add shadows to make the figure appear 3 Dimensional. In the hair, I used the same technique as in Step 3-4, to gen nice crisp edges.
To make the figure have more depth, add highlights. There are subtle highlights in the flesh made by the air brush tool. Make sure the Highlights correspond to the Shadows.
Making sure that it is logical helps your piece look better. The light source touches only the top surfaces.
Try to avoid making shadows with black in normal lighting. It weighs down the piece in an unnatural way. Try darker shades of the base color. Same goes with Highlights. Try to avoid White, use a light version of the base color.
Trace the figure using the Straight Line tool for crisp clean lines.
I added some Air Brush highlights to the hair.
Lastly, I added some more highlights and shadows to the body. Dark Purple at Low Transparency is a good color to shade skin sometimes.