Strange Goldfinch

This bird was a normal Goldfinch in many respects (size, song and markings) but it was an extremely dull bird, the yellow on the primaries was washed out and hardly discernable as yellow and on the greater coverts it was more of a dull orange/buff. Where the crown should be red this was showing greenish-yellow. I released it without ringing it.
Mick

Looks like it is perhaps slightly leucistic or there is some similar sort of problem with the pigment cells. Could be a natural defect or possibly due to breeding and thus would imply bird is of captive origin. Anyone else care to comment?
Pete