Like I said before, what colour is the rooster (americanas come in a lot of colours) I could plug the rooster and the hens in to a chicken calculator and I could tell you what you could get in the rainbow of chicken colours
Americanas definitely come in lots of colors - Ameraucanas, though, have a set color variety per the breed standard. The difference would be fairly important given that if the bird is not true to breed standard/a true Ameraucana that will play heavily into the results of any pairings that are made.
OP - can you post a picture of your rooster? "White and brown" isn't giving me a very clear fix on any one breed standard accepted variety/color.