I've been researching and asking around about these brown chicks that are be popping up - based on consultation with two individuals.......a reputable Giant breeder and a second longtime breeder who is also a judge and who specializes in genetics, they state it is apparent another breed was used (most likely dark cornish) in relatively recent breedings as the breeder apparently hoped it would be an improvement for their particular flock, and that's what this brown color and barring is that is popping up.
My hope would be that folks who do this would let their customers know, though....as it's NOT common practice, and not being honest about it puts us ALL behind - at least those who try to do the right thing by buying from good breeders. While the APA Standard notes that Cornish was added to the line in later years, it's a huge responsibility that a breeder takes on to bring a different breed in. Particularly, when the chicks, down the road, are then sold for profit or otherwise scattered throughout the community and represented as "pure." It also introduces NEW problems that weren't present before..........as if we didn't already have enough going on.
Such practices are responsible for problems like pale or pink underfoot color, pink skin color, the loss of feather quality and richness in the black color and tourquoise sheen, and general size and type issues for the blues. The resulting chicks are further propogated by well-meaning but uninformed people, as well as the consequences of the new breed addition. This could very well even be the case for the last breeder who may have brought "fresh blood" in by buying a breeder Giant from another breeder, not knowing the (non-Giant) genetics the bird carries. It is one of the reasons you find practices by some breeders who maintain closed flocks and "pure black" strains with their black Giants, including the breeder I do business with.
Sorry to sound like a wet blanket, but it's imperative that good information gets out there for those of us wishing to do right by this breed. Just sayin'.