Depth Cues: Creating the Illusion of Depth - Flash 3D: Animation, Interactivity, and Games - page 45

Figure 2.47 Gradient Transform tool
Step 8: Paint the surface shading
With the Brush tool selected from the Tools palette, move the cursor over the head.
Click and drag to start painting the surface shading (Figure 2.48). When you are done
painting, release the mouse.
Figure 2.48 Painting the surface shading