Why do I have a Brown Chick?

[Seth_12]

I recently hatched some olive egger chicks that came from black OE hen and a blue OE rooster. The parents stock came from a breeder who used black copper marans and ameraucanas for their olive eggers. I know that in BBS genetics, when you cross blue and black together you'll get 50% black and 50% blue. The puzzling thing with one of my chick is it's brown while the others are black and blue. So I'm confused on how I got a brown chick. Has this happened to anyone before and if so what did the chick look like when it got older?

The brown chick is the one to the left.

 

[Auntiejessi3]

I hatched some OE's with my Wheaten Marans roo and my black F2 OE hen, from the folks I've talked to there must be some birchen hiding somewhere (probably in my hen) Onyx-hen and one of her pullets. Most of her chicks hatch chocolate colored and get this pattern, I think 2 have been solid black