What color pitbull do you get when a black pitbull and blue pitbull breed?

You will get the same breed you started with an American Pitbull Terrier. If you are referring to what color you would get, then you should look at a breeding color chart. Breeding for color in a pitbull or any breed is not responsible. You should also consider things such as family ancestory, and defects within each dog. But if both are good solid lines, then breed away. Just make sure you know what you are doing, and make sure you are making a positive impact to the breed.