My friend has a male blue rat that she wants to breed. (I believe she wants to breed for feeders as well as holdbacks)

I'm giving her one of my unbred females. Neither are ready for breeding just yet, but will be in the next month. One is a berkshire and the other is a black hooded. I was wondering what colorations and markings either of those breedings will produce. I've never had a blue in my colony so I have no idea how the genetics work for blues.