Here is the base close up with the picked colours. I think it is always best to prepick your colour before you start drawing the hair.

Outline of the hair you want. Right now the hair outline is pretty messy, so you got to clean it up to one pixel.

Now the hair outline has been cleaned and the colour (indicated by arrow) has been filled in.

Now add the next colour, this is the basis of all highlights. Notice that the highlight is drawn in zig-zag? It is because there's no such thing as a straight highlight on hair since there is many strands of hair.

Now add the 2nd darkest colour. This should only be at the hair parting area and tips of the hair

Now continue the highlight in the same zig-zag manner.

This should be the lightest colour of all, and you should draw it in zig zag too but unlike the other too, do not make it too wide.

This is where it gets complicated, to give your hair a realistic look you should follow this step, otherwise you can stop at the previous step. We are going to eliminate the outline by colouring in the colour that is beside the outline. DO NOT eliminate the hair parting outline and the tips of the hair

The Completed doll.