As I mention, knowing your color theory and anatomy is vital to painting skin well. Someone has already asked for resources on color theory, so it seems logical to post this list in a journal so everyone see it:
Color theory tutorials on the web:
Those are all great starter tutorials. For more in-depth theory, look around on amazon.com for books on the subject. I am sorry but I don't know any to recommend. And of course, if you can try to take a class on the subject!
If anyone has other good resources or recommendations, link me and I'll add to the list.
Cheers