Yes, PLEASE keep the blue-bred blacks separate with permanent identification. It's fine to use black coppers in a blue breeding program, but not the black birds that come from blue breeding into a BCM program.Keep the Cuckoos pure in color. You can breed the black copper and the blue copper together if you want. I don't think the Blues will ever be standardized. Make sure you keep some pure Black Coppers so you have somewhere to go if you get tired of the Blues. If someone is buying Black Copper, great odds are they don't want one from a blue background or breeding. JMHO.
Best,
Karen