Dumbo is a simple recessive. I don't know if you can have a mixed litter sired by two different fathers. I know it's possible in snakes, but I'm not sure how rats would work. I'm not entirely sure about that.

As to the litter of dumbos, I have an entire litter of dumbos from a dumbo x dumbo breeding. They're all either blue or siamese! Well, there is one black girl, I think she's a keeper!

Oh, I have a dumbo named dumbo. But she's russian blue, so it was fitting. I also have a Gumbo, and a gumdrop that are both siamese just to make things confusing!