I don't have a lot of chick pics of the Marans but they did not look as you describe in your post. They had the typical tuxedo. I do not think the breeders of the eggs from which these birds hatched would have mixed the birds. I will think about letting them grow out but the leg feathering on these two is minimal and that is a culling point for me. The blues are hatching out with better feathering. I have other ones growing up that I will watch and see what happens. My rooster has a white feather on his toe that I had hoped would molt out but it seems its coming back in and maybe another on the other foot. I'm rehoming him and will have to source a different BCM if I decide to do a Black Copper vice a Blue Copper.