He looks to be a blue born yorkie. If you look at the link that was posted, they show a picture of a blue born yorkie and he is the exact same color as your boy.
It is said that blue borns aren't healthy, they will have health problems, if you have a blue born without ever having these problems you are lucky. He might seem healthy now but that may not be the case when he gets older. I agree that the parents shouldn't be bred again and that you should not sell this pup when he is old enough.
Sorry about the little boy, hopefully he will be one of the lucky ones to live a long healthy life.
Congrats on the litter, I can't wait to see pictures of them as they grow up.
