Do you mean one rat has a ruby eye and a black eye? It's just a pattern difference(yes, pattern) and is called odd-eye.

Ruby eyes on a black rat is called double odd-eye. I have a beige wedge-blazed capped boy who has a pink eye and a brown eye. He is aptly named Funny Face. He's a doll.

Again, I have pictures! Lemme get around to it, LoL, and I'll get them on here.