Judson,
Your problem is not painting particular skin-tones. It lies with your overall lack of knowledge of the underlying structure of what makes a good painting; good solid drawing and an understanding of the basics of form.
I would suggest you look into buying Harold Speed's books -
"The Practice and Science of Drawing" and "The Practice and Science of Painting". They are only about $12 each.
Practice ONLY your drawing for at least a year, then do some simple monochromatic painting of simple objects before you attempt the human face and painting in full color. You will be glad you did.