Usually it is the other way around, that the pullets lack coloration, not the cockerels. Getting birds "accidentally", because someone included them in an order but you did not order them, is a dangerous way to end up with more birds/breeds than your infrastructure can handle
Just a thought! That said, if they are otherwise nice birds and decent type for Black Copper Marans, you could hatch a few and see how they turn out and how you like them. The black cockerel will be genetically black copper even though he is not expressing the color. I'd also look at them really closely to make sure they are pure Marans and not a mixed breed, like olive egger. There have been so many posts of people getting mixed breed Marans mutts it seems. Some of those crosses can look like pure Marans but you'd know for sure once you hatch from them by the looks of the offspring.