Vicki, I see that the female Marans in the pictures have nice dark Soft feathering. The young male looks to have the unwanted Brown soft feathering below the vent area. This will breed forward if it is indeed brown soft feathering.
He is from a black to blue copper mating and was thinking of using him with the blues. Think it would throw a hitch into the blues? His mother is a big ol' beast, but don't want to muck up the blues if the brown tone will affect them.
Also on your comment previously about the back being off on the back of the BC...you mean the cockerel? I caught the photo as he was coming out of a dust bath, but I'll catch him up and give him a good look over and see