Let's try adding highlights and shadow to hair we have drawn. "Add" blend mode can be used to express light. Similarly, "Multiply" blend mode can be used to express shadow.
Open the ① Layer window and on top of the base hair gradation tap ② New Layer. Finally add a layer for highlights.
Tap ① to make the layer you added the Current Layer. Next, tap "Add" to open the ② Blending Mode menu. Finally select ③ Add from the Blending menu.
Next, tap the ① Clipping button and turn on clipping.
Set color to white and select ① Airbrush (Triangle) brush and set thickness to ② 70 pixel.
Paint with a fat airbrush.
Since we are separating the layers, we can also change the intensity of the highlights. We can weaken by decreasing the ① Layer Opacity slider. Here we have lowered it to 70%.
Similarly, tap the ① +button in the Layer window, add a layer for shadow, make it the Current Layer, and set the ③ Blending Mode to "Multiply" and finally turn ④ Clipping on. Also, change the brush color to black.
We will now add some shadow. We can adjust the darkness of the shadows by adjusting the shadowing layer's opacity. Here the layer's opacity is set to 30%.
The above figure shows the highlight and shadow using the "Add" and "Multiply" blending mode.