Sooooo there's occasions in nature where animals are born with reproductive parts of a twin they consumed in the womb. This causes the animal to have different DNA in those parts, meaning they could show one thing. I'll use cats as an example. Let's say a tom has ginger fur, but their reproductive DNA is blue. They mate with a ginger molly, the kittens come out dilute tortoiseshell. I think this mutation could be fun here as it would be almost a total surprise on what you get. Though you would be aware of the mutation and the genetics that are in those reproductive organs. This also happens in females too. The genes could even be editable with a special applicator.