Start with the head however you want.(I'm starting with a sketch instead)

Add another layer.

Sketch the front hair.

Sketch the back hair curved inward.

Add a new layer for line art.

Choose the color of the hair.

This is a guide to the colors!

I'm choosing brown

It should look like this so far.

Turn off visibility for the sketch layer.

Add a layer underneath the line art.

Color it in with the base color.

Add highlights and shadows

This is what the finished result should look like!