Natural looking hair

Dark gray base color, black wash, dark gray lightened with light blue for highlights.

 

You might also try orange for highlights (trust me, that's straight from Shep Paine himself). If you're doing blonde hair, start with olive drab as your base and use a tan or khaki for the mid tone, with yellow or yellow-tan and then white for highs. Brown can go many directions, depending on what shade. I'll have to go into that later, when I have more time.

Thanks for your help, guys. I'll be trying these techniques soon. I'll let you know how I get on.