The whites are a recessive gene that has popped up from these imported lines . Kind of like a red headed child popping up in a family . Likely the recessive white has been there since the breed was created . Cold tolerance is good . However the rooster's comb will freeze in very cold weather .
This is the type of color that I get on some recessive white Ameraucana . Three feathers total on this cockerel . Easy to overlook if you are not looking close . 2 copies recessive white .
This hen has 1 copy dominant white . Big difference .
This may help someone tell the difference .
Recessive white often have a stray colored feather . My experience is with white Ameraucana . The stray color is hard to notice and minor compared to 1 copy of dominant white ,