Teresa,
As the current research believes, it is genetic in fact in a reseach
feature in the news notes of Cornell Lab of Ornithology magazine
"living bird" showed a UAburn graduate student testing out a theory
that the pigment of the house fiches related to the amount of
carotenoids (the same compound that give autumn leaves their bright
colors. Possibly these males might be eating from different food
sources in the neighborhood. The clip didn't mention how long the
certain pigment might stay wih a certain male house finch. If anybody
gets living bird this was the winter 1996 issue, and if not I can
type it out on the net (its not very long) for interested parties.
-Scott Downes