So if Yellowface I is double factored, it creates a white face.
What happens if you managed that in greens? It would be a lot of guessing as to which greens are yellow faced and you'd get a lot of blues thrown into the F2 offspring so it would be a complicated process, but has anyone tried for it? Would it override the natural yellow base in a green?
Look at me, I don't even have budgies yet and I'm all about the genetics.
There is supposedly a new mutation being called White Cap in budgies. It's a yellow based bird (green) with a yellow face as usual, but the cap is all white. You should be able to find an article about it if you google it. But it has nothing to do with the YF genes at all. And I don't know if it's entirely true, so take it with a grain of salt until someone like Lindsey comes along and says otherwise.