I would have bet a million dollars it was a breeder. SOP at its best. It is not the brown gene. With a mask that would be called chocolate. That is not what it is. It is a rusty black. Porters site talks about rusty blacks in the article on Jersery buffs. They are a mix that does not breed true. Porter also has pictures on his genetics board.
A tip to you. When he is breeding age keep him away from your slates unless you want poults that look like mud.