Ah, right, I understand.  Hmm, for that you really have to learn how to actually PAINT skin.  That's a much more complicated topic.  You have to know about skin tones (luckily not about shadows, as that's done for you ;) ) but you have to be aware of seams, and aware of when you place the cuts, where they will end up on the model after it's been wrapped round the mesh.

http://www.students.yorku.ca/~harnock/tutorials/skin.htm

This is good for learning the basics of painting.  As for cuts and scrapes and grime etc, I think they will have to be painted on in postwork.