I think it is all about genetics. If it helps, this run on Marans are from the Cottage Hill line. That is about all I know. I have been reading up on them as much as possible, and I think this is some coloring that is considered undesirable. If you ask me, she is cute as a button and has a wonderful personality. It has won me and my hubby over in a big way. She is soooo very spunky for a runt!
One of the other things I found out is that the daddy is a HUGE BCM Roo and I looked at him yesterday. There are BCM hens in the same pen as well as a couple of Americauna's. I purchased two Olive eggers from the breeder too, which came from the same daddy. The hens in that pen were both totally black as well as black with the copper around the neck. They were very beautiful birds.