If you cross a brown egg layer and a blue egg layer, 99% of the time, you'll get a green egg layer, yes. Now, if the progeny comes out with a single comb, there is a higher chance it will lay a brown egg, but most of that cross does seem to come out with a pea comb or a modified pea comb. My Panda, who is Riley's half sister (same Ameraucana mom, different BR sires), lays a light olive green egg. Panda is barred, with white legs, but has no beard. Riley lays a lovely bluish green egg, has yellow legs and a nice beard.
I think you'll be quite pleased with the cross. In fact, it's my favorite cross.