It will be very obvious about 8 weeks old - the combs start getting very red on the boys and shortly thereafter I believe the adult feather pattern shows up. Your brown one does look like a girl so far.I really hope the plainer one is a pullet. She has a very narrow comb.
About what age do you think I'll know?

Quote: You got it right! It doesn't matter which parent the gene comes from, but it is easier to see if it is there on the hens... If the boy is from a blue/green/olive egg he will carry one for sure. If you cross them and get a boy from a blue egg, you can use him back over his blue egg laying mother and perhaps get the double dose of O/O (blue egg gene) for future generations.
The only other consideration is if the blue egg gene carrying parent has one or two copies of the blue egg gene - that is the only way it would skew things one way or the other. Most of the Auracana/Ameraucanas have two copies, but that is not a given. If you want a nice array of colors I would keep one Auracana rooster, that way you can make sure you have the blue egg gene somewhere to replenish. I would keep one Barnvelder rooster for the dark side.. of course I am sort of partial to the way they look![]()