Asking questions proves you are not stupid.
Blue crossed with black either way statistically yields 50% blue and 50% black. Breeding a blue copper Marans to a black copper Marans will get you BBS copper Marans (blue/black/splash). It is suggested NOT to breed a blue-bred black into BCM lines, but it's fine to cross a BCM into your blue copper lines to improve type or egg color or whatever. Just know that any resulting black chicks are not BCM but blue-bred blacks (BBS copper Marans).
When I read back over that it is clear to me, but if anyone can say it clearer to help out clankeyes please chime in.