You can use any colours for hair but for dark brown as in this image I used...
A light colour for the blender i.e vanilla
A little bit darker i.e Caramel
A medium shade i.e burnt sienna
A dark shade i.e walnut
With hair and clothes you just need to identify highlight and lowlight points. In this example the highlight points on the hair look like bumps and the lowlights are dips.
Colour in your hair with your lightest colour (VANILLA) and leave the highlight points white as shown below.
Next take your little bit darker shade in this case CARAMEL and colour over nearly all of your base colour (VANILLA) leaving just a little bit showing.
Take your medium shade colour (BURNT SIENNA) and colour over most of your image again leaving part of the previous two colours showing.
Go back to your lightest colour (VANILLA) and colour right over the hair again and push the darker shades gradually into the white highlights you left. With a large highlight do this gradually and leave some white showing still, with a smaller highlight run right over it with the vanilla as seen on the smaller highlights at the bottom of the hair.
See how the vanilla washes the colour out and starts blending them together?
Next take your darkest shade (WALNUT) and colour onto the hair leaving quite big bands of the blended colours showing as shown below. The darkest colours really spread out when you blend them so if you only leave a small highlight point, when you blend it will drag too much of the dark colour over and disappear.
Blend this in with the VANILLA again pushing into the highlight points gradually.
Add more of your darkest colour and repeat this as necessary and continue blending in with the vanilla. I usually do this 2 or 3 times then when I'm happy with it I completely cover the white bits once with the vanilla and touch up the very lowest points with the walnut.
Here the hair is completed covering the white completely so that it blends in completely and looks quite natural. If you wanted to do blondes, reds, blacks or lighter browns just follow the same principal of lights, mid and dark so light blonde hair for example you could use ivory, primrose, buttercup and vanilla as the darkest.
You can also drop the 2nd lightest colour if you wish (Its a personal preference of mine as a way of making the colours more vibrant) so could do this without the caramel for example and just use vanilla, burnt sienna and walnut.
Blue hair & fantasy film wings with lots of sparkly bits added with a glue pen and glamour dust.
Hope you've enjoyed the tutorials and if there is anything you get stuck on just shout :)
Have a play with your own colour combos to find what appeals to you so stamp yourself some images out and just colour in a part of hair and write underneath what colours you used as if you like it you'll remember next time.