Brown and black baby squirrels in same nest?

I have a hollow tree in my yard which a squirrel has built a nest. The mother is a large brown squirrel. However now the babies are sticking their heads out of the holes in the tree and running around the outside of the holes and I see that their are 3 blacks ones and 1 brown one. How can this be?Brown and black baby squirrels in same nest?
mixed genes from both parents.


the father is most probably black as well, so his colour was more dominant in those particular baby squirrels than in the single brown one


the mother's brown coloured gene was more dominant in the single brown baby squirrel than in the black ones.