finch feathers discoloured or changing colour - unsure

by Deanne
(BC Canada )

my very white male finch appears to be changing colour from his low back through his tail feathers - they are turning fawn - ish, almost a pink ? When he came out of the bath yesterday he was ruffled up and preening and it looked like there might be something under the feathers of his lower back - a wound or scab maybe? they do occasionally bicker but he is bouncey and singing and has a good appetite - I could catch him but it stresses them out so much I would rather leave him to heal by himself - he is not losing any feathers and does not seem to be worrying at it -what do you think ? have you heard of this before ?