Hi there! While I don't see a specific question I'll assume you are wanting to know why the variance in leg feathering and egg colors in the offspring of your original flock of Marans. I've got two French Cuckoo Marans and in my Marans breed research prior to getting them, learned two things related to your concern. First, there are both clean and feather legged varieties, with the English preferring the clean they are allegedly the most common found in UK (Copper Marans) and were purpose bred away from leg feathering. The French version has the feather legs and likely your birds have ancestry of both versions and thus no feathering on legs in that particular bird. It's just in the genetic background. You said you have Copper Marans not French Copper Marans. Given your flock is from UK they are likely a mix of both, but here in the states a Copper Marans would indicate clean legged. Kind of like the King Charles Spaniel and Cavalier King Charles Spaniel. Both similar yet very different breeds and the one word difference in the name is of no consequence to those unfamiliar with the breeds and people quite often innocently use the wrong names in my experience.
As for egg color, despite all the gorgeous chocolate colored eggs seen online, there is a wide scale of brown possible. It takes a very diligent breeder who selects only the very darkest brown egg layers for their breeding program to produce consistently darker scale egg layers. There is a breed standard for the French Copper Marans eggs. Even so, there's no guarantee on the colors, which actually progressively lighten over time until she goes through molt process which somehow hits the reset back to her darker pigment eggs. Perhaps the clean legged gene may be tied to the lighter eggs also? I'm by no means an Eggspert as I'm new to them myself but perhaps some Marans breeders here can better eggsplain.
