Hi ,,,!!
Yes I have 6 mixed breeds hen , 7 rhode island red hens and 2 roosters and yesterday I bought a pair of black copper marans (French) they are 5 months old And I just love them !!
I decided to buy them because I'm crazy about the egg color I loves brown eggs and my RIR lay light brown eggs not dark like the marans
I used to have some Cuckoo Marans and the Marans certainly do lay beautiful chocolate eggs. Good luck with your flock.
and Welcome To BYC! BCMs cockerels usually do get some color in their hackles by five months, they do come solid black, so like you said, maybe you got a black pair.