Ameraucanas are 'supposed' to lay only blue eggs, but somefamilies/varieties are known to lay off colored eggs. Hard to tell what color egg they lay in the show cage.
Sourland, you're getting nitpicky again. There is a difference in show birds and purebreds. The judge can only judge by the traits he/she sees. Some people breed only for those traits. To me, these are not truly breeding purebreds. The judge will not see what color egg the chickens lay, for example, whether blue or green if an Ameraucana or how dark brown for a Maran.
The purists breed for the traits the breed is supposed to have, not just the traits the judges see. I seriously doubt people are going to sell prize winning Ameraucana strains that lay green eggs. Their reputation would quickly become known if they did. And there are plenty of breeders doing it right that do not sell their eggs or chicks for their own reasons that have nothing to do with green eggs. I'm not talking about them. But yeah I'd be really disappointed if I bought what was supposed to be an Ameraucana from a breeder and it laid anything other than blue eggs. I don't count the hatcheries in this. None of them that I know of sell true Ameraucanas. Even if they started with true Ameraucanas, they pen breed and mix the colors. And some mix in other breeds to get prettier colored chickens or better egg layers. You will get green or brown eggs from these.
I don't know if this story is true or not, but it was posted on this forum a couple of years back by someone I pretty much trust. Since they say they tricked a judge, I won't say they I totally trust them. They said they crossed two different breeds and got a rooster that was not disqualified when shown as a New Hampshire. Neither parent was a New Hampshire. It did not win, but it was supposedly not disqualified. Anybody with the courage to trick a judge they might see again, well I would not do that. But this illustrates that a judge can only go by what they see.