Baby Born With Colored Hair?

This isn't an issue but more like a... How? Why? 

The mom had black hair and the dad had brown hair but the baby was born with naturally pink hair and eyebrows. How?

The only thing I can possibly think of to explain this is that she interacted with a fairy and was sick during her pregnancy - I don't know if one or both contributed to this? 

I tried searching it up to see if I could find an answer but so far I haven't found anything solid to explain. I don't recall any of my mods having an effect like this and it's never happened before. I'm not complaining because it's actually really cool, but I'd like to know how it happened lol.