My 3 month old son has blond hair except for a small patch of dark hair on top of his head. At first I thought it was a bruise but it's been there at least 2 months now. I've pulled back the hair to look at the scalp and the scalp is the same color as the rest so I know it's just the hair.

I'm not really worried about it, just more curious. I'd like to know if it has a name and what causes it. I've read about people having white hair or lighter hair amidst dark hair but never dark hair amidst light. Anyone??