What's difficult with thinking the zone system in colour, is that caucasian skin is traditionally placed anywhere from 5-7 depending on lighting conditions. For a more somber image in black and white, say in a dark room where a white face is the highest tonality, ZV can work a treat. In colour, I think you can get away with a certain amount of tonal experimentation with white skin, but feel it's difficult with very dark skin in particular.

That said, I've been looking at an African photographer recently, please take a look - http://www.vivianesassen.com/#/flamboya - The image of the woman sat on the tree in this series ('Spring of the Nile') is particularly striking. She works with shadows on her subjects to great effect.