I have a villager that had a head transplant! She had dark, dark hair. It was sooo black that it almost looked blue. It was in those Princess Leia twists. Now it's in a ponytail, and it's auburn!!!! What happened??
Here are some pictures. The SAME GIRL!!

There is an island event - actually two - where this could happen. Had you just clicked something in a decision box?

Well, there was a vial that she drank and then didn't quite feel herself...

Yes, that's one of them. When you click that, the villager gets a different head.

Oh. That stinks. Well, a new child was born recently, a girl with the same head as the other villager had. That sort of makes up for it....