AJ's Weird Problem

A few weeks ago, we noticed a black spot developing on AJ's skin. His hair started falling out, and I started to FREAK out. We took him to the vet, but since his skin and hair were both healthy, she told us not to worry about it, but to just keep watching it. After we had him groomed (and...he bit the groomer again) we noticed that his hair was growing back in that area, but it is black. It is so weird, because it is really coarse, and nothing like the rest of his skin. It doesn't seem to bother him at all though, so hopefully he's okay!