After you have colored the hair, add some highlights and shadows. Add is good for highlights and Multiply is good for shadows.
Open the Layer Window, tap the Paint Layer for the hair base, and tap the + button to add a Highlight Layer.
Tap (1) to make the layer you have just added the Current layer. Next, tap the (2) Blend Mode that reads ‘Normal’, select (3) Add, and then close the Layer Window.
Select the Magic Wand from the Tool Selector and use it to select the hair. Check that the Magic Wand properties are set to Color, 10%, Specific, Basecoat Layer, before using it.
Set the color to white, select the Airbrush (Triangle) and set the size to 70px (pixels).
Paint with a thick airbrush.
As the layers are separate it is possible to change the strength of the highlight later. Decreasing the (1) Layer Opacity slider will weaken the highlight. Here, it is set at 40%.
In the same way, tap the (1) + button in the layer window and add a shadow layer. Set this layer as the (2) Current Layer and the (3) Blend Mode to Multiply. Set the Airbrush color to black.
Stroke the airbrush horizontally between the highlights.
By changing the opacity of the Shadow Layer you can adjust the strength of the shadows. Here, the layer opacity is set to 67%.
The above shows a finished example where Add and Multiply have been used to create highlights and shadows.