CMs versus BCMs

[PaulaJoAnne]

Can anyone tell me the difference?
I have 5?, what I was told were CMs, and they lay what I would classify as a medium dark egg, compared to what I know the super dark eggs to be.

 

[Mahonri]

Cuckoo Marans aren't known for super dark eggs.

French Black Copper Marans and Wheaten Marans are known for the darkest Marans eggs.