The high-contrast effect of black skin seems caused by differences in collogen/oils and pigmentation versus caucasian skin. Much more difficult to control so broad lighting, as you say, as well as other more "cosmetic" approaches are often in order.

Here's an interesting example of what I'm talking about (especially the second photo)... to help anyone who has not yet experienced this. Although this is wet-plate photography vs regular film... the effect is quite the same:

http://www.largeformatphotography.in...l=1#post917720