I had a similar issue with clothing.  It would turn the mannequin skin black.  I had some files that were pulling the wrong textures for some reason.  They would pick up the texture of another skin/clothing file and try to use it.  For example: 

  I ended up doing just what another poster suggested.  Going through my files a handful at a time and narrowing it down to the bad files.  It took several days but it fixed the issue.  Point is, your problem looks like a similar issue only with hair.