My whites stay clean, I have white turkeys too. I also have a big white dog so that could be why I don't loose them. He is a very good guardian dog from ground or air attacks.
As for keeping Guinea in a cage.. I agree with everyone else. Its not the best idea. They are wild birds at heart and really do need to fly and chase bugs and run. The point of having Guinea is to eat bugs, and they can't do you any good, or you do them any good if they are locked up. Its almost mean for this bird to not get to run.