If you use the black over a lighter blue, he will improve the color and lacing in some of the cases. Breeding blues is difficult to get that perfect balance between a perfectly clear slate blue ground color and then a nice strong edging of black on the feathers. Good luck.
So your saying if we have a blue rooster we need to breed to black hens in order to get blues? Or black rooster to blue hens? If you breed blue to blue, you'll. Get nothing but black chicks?