Hair Painting Brush Instructions:

You get to make your own brush, then save it as a custom brush variant if you like it.

Paint a head of hair, any style, any colors, but try to make it look somewhat real. 

I'm sure you'll do better than I did in these illustrations. They're just meant to give you an idea of how the brush can be made to paint. 

1. In the Art Materials palette's Color Set section, create a New Color Set containing only two or three colors you want to begin with in the hair. (You can add 
or delete colors from the Color Set later as you work to build up the hair painting.) To create a Color Set:

In Painter 6:

Click the New Set button, choose a color, then click the Add Color button. To delete a color, first click the appropriate color square in the Color Set, then click the Delete Color button in the Color Set section. When you're asked if you're sure you want to delete the selected color click the Yes button. To save your custom Color Set, click the Library button. When you're asked if you want to save changes you've made to the current Color Set, click Yes, then give your custom Color Set a unique name not used by Painter and click the OK button.

In Painter 7:

Click the New Color Set icon (first icon on the left), and choose Create New Empty Color Set, choose a color, then click the Plus icon. To delete a color, first click the appropriate color square in the Color Set, then click the Minus icon in the Color Set section. When you're asked if you're sure you want to delete the selected color click 
the Yes button. To save your custom Color Set, click the Library button. When you're asked if you want to save changes you've made to the current Color Set, click Yes, then give your custom Color Set a unique name not used by Painter and click the 
OK button.

2. In the Brushes palette, choose the Brush's Smeary Bristle Spray variant.

3. In the Brushes palette's Variant menu, choose Restore Default Variant.

4. In the Art Materials palette' Color Variability section, choose "from Color Set" from the drop down menu.

5. In either Brush Controls palette's General section or the Controls:Brush palette, move the Opacity slider to about 66%.

6. In the Brush Controls palette's Size section, move the Feature slider to 
about 4.0.

7. Brush with light pressure to begin blocking in color, then apply more pressure to begin defining individual hairs more. (As you press down, the individual bristles paint darker so the "hairs" are more evident.)

8. Adjust the Opacity and Feature sliders as needed to get the result you want.

9. Add or delete colors to/from your Color Set as needed to create a natural variation in hair color, and to create shadows and highlights or a sun bleached hair look. 

10. When you're finished painting the hair, zoom in and give it a "hair-cut" to trim 
off any scragglies (stray bristle marks) that extend beyond where you want the hair 
ends to be. 

I've been playing with "hair painting brushes" for a while and like the potential of this one very much. There's a lot of leeway when using this brush to build up the hair and hair colors gradually and also paint over areas that don't look so hot on the first, second, even the third tries. 

If you're used to painting hair, though, this should be a breeze for you. (Feel free to chuckle at my less than wonderful examples.)

Have fun!