the green is automatic yellowface they can't be yf2. only blue birds can be yf or yf2. Its just not possible for a green that automaticly has a yellow face to be a yf2 trust me, I asked nev90 and he said pretty much the same thing lol. that would be like getting a white faced blue. its automatic, so its just not possible lolI might be wrong..but yf2 is also dominant, so unless the green is split for blue, you'll get 50% yf2 greens, and 50% green normals. If the green is split for blue, you'll get yf2's, and normals..blue and green.
It's the double factor type 1 yellow face birds that have a white faceAbout greens not being yf2...I've heard that yes, greens can be yf2, but of course since they have yellow faces already, it doesn't show up until you breed them..and I think double factor yf2 means they have a white face, on blues..but I'm probably wrong of course..:S