It could be old feathers he may be getting ready to molt. I have 2 blue roosters that have some blue in their feathers suddenly. I know these are excellent show quality birds with no red leakage or mix in them. We live in Florida and they get their feathers sunburnt when the feathers are old. They should disappear when he molts. I raised one of my roosters from a chick. He was always a dark dark blue until lately you can see some of the brown coming through. I asked around and was assured it was old feathers give him some time you maybe pleasantly surprised.