It's exactly like dog breeds a male Chihuahua could impregnate a Great Dane female. If you breed a green egg breed with a brown egg breed you end up with Olive Eggers.
It may be difficult for a Serama to breed with a large hen but technically it can happen. Rumpless Auracana have difficulty breeding as far as I know they are the only one's and it's just due to being Rumpless.
I ordered 25 chicks and got 27 last April and they are all still health and laying well I'm very happy with my birds. I will say they are a bit small but other than that they are good birds,with the exception of the Black Sex-Links I don't really care for their looks or egg quality but, the Red...