If you are looking for texture imperfections, then you would be better off using brighter lighting, but too bright will wash out details. A solution would be to temporarily raise the brightness of the texture in the Material Room and check for imperfections or problems, then reset everything for final release. Very dark skin is problematic because details are lost under normal rendering conditions. The introduction of specular maps for highlights can alleviate the detail loss; however, how realistic do you want the character to appear in the final render? Chances are a user might strip out all your Material Room settings and replace it with their own custom creation.