With dark skinned people, as with dark tuxes, black dogs, or other dark material, it's not how much light you blast them with from the front that brings out the detail. It's how you light them from the side. Side like is used on dark people to create the specular highlights that lighter skin reflects with frontal light. So if you can, meter normally (or maybe a 1/2 to 3/4th over) and skim some light across from the side. Either reflected light, a off camera flash or side sunlight. This is the same for a white wedding dress. If you skim light across the front of it, you will bring detail out that you won't see with just frontal lighting.
Mike