In real world photography you light dark skin exactly the same as lighter skin. If you add more light to get details then everything else gets more light too. You can use lights at more of an angle to bring out details depending on how close you are (head shot vs head and torso etc). Very light skin displays the same phenomena but in the opposite direction. On both light and dark subjects (if properly lit and exposed) the details are still there, we just don't notice them as much, especially if other items in the scene are more of a neutral or median brightness.