@cal, I know you say that only a few will turn white, alot of people do. But where is the proof of this?
All the adult xingus I have seen have been white/gray, both pics from the hobby and from the wild.
I just have a feeling the white type is so rare only because pretty much no one owns adult specimens.
but maybe you have not seen the post on mfk a few years back when a fellow out in europe bred xingus and his breeder sized female was not white!