This is a picture of my Hatchery bought Fav, at first I thought she was a he with all the black! She is A She and Purely Fav. Yours might not be a Mix It might just be a off color type Hatchery Bird like mine! I call mine a Sport Fav. On the fav thread they tell me its common for Hatchery birds to have off or darker coloring.
Mine were slender up until the new winter feathering!