The old feathers will off color shortly before molt. Wait until after he molts before doing anything drastic. I've found that the self blues turn this straw yellow, blues turn red, and blacks turn a rusty brown, then they are good again after new plumage! The main thing is that he didn't have any off color at 5 to 6 months of age-if so that would definitely be leakage and he should NOT be used as a breeder. If the straw yellow starts developing at 10-11 months of age its old plumage getting ready for molt.