Bob, Leucism can affect any part of the body and is blotchy. It can affect one feather or the whole bird. I have a number of birds here, from Hummers to Cardinals and sparrows that have Leucism. One family of hummers I've watched show leucism in the females and is progressive from one generation to the next.
It can also affect animals. Albinism is debilitating, depending on the degree of it, so I think birds, with the hard lifestyle they already have, will not survive long with Albinism, while Leucism has no bad side effects at all, other than maybe making it hard for a bird to find a mate, if it looks too different. 