In this case, you only need 3colours.
Step1:
Use the lightest colour to outline the shape and separate the hair zones.
Remeber to sharpen your pencil to make the lines thin.
Step 2:
Fill all basement colour.
Step 3:
Use the darker colour to highlight some area.
Step 4:
Use the black or darkest brown to refine the dark area.
Final:
Use black colour to finish the head colour and some shadow area.
Done