I have to share.
I bought three baby Timneh greys from a friend for hand raising.
The oldest is starting to pin on the wings and there are some feathers popping on the wings and tail. In a book called A guide to Parrots as Pet an Aviary birds a mutation is listed, but only for a Congo as A White-Tailed (Blue).
Yes, the oldest is going to have a White tail or some white in its tail. I cannnot keep all three, if they are all the same, but definitely I will be keeping one of them.
I have informed the breeder.