LEUCISTIC is the word you are looking for.
This is not albinism (ie white with pink eyes), but involves variable amounts of white, whitish or pale plumage. 'Pale' (ie slightly leucistic, washed out) birds seem to be recorded quite rarely, although with pale plumage and white wings and tail, such birds are near the extreme end of the scale, although, sometime there will be a pure white bird, with dark eyes, the extreme on the leucistic scale. The paler hard parts would be part of the same phenomenon, and the more rounded heads and larger size perhaps a 'trick' of the pale-colours/light or a 'fluffed-up' posture? Leucism is a genetic characteristic resulting in a partial loss of pigment. It is rare amongst wild birds - total pigment loss (albinism) is more common.
(Source:
http://www.mullbirds.com)
Tabbyman's Chaffinch (ScotBird Gallery #831) is a good example of a part-Leucistic bird.
Regards,
-Mark
