self blue cockrel has developed tan wing feathers

[Gagirly]

I'm going to a show in a month and have been looking closer at my birds to decide who to take. I have a self blue d'uccle that's almost 7 months old with nice confirmation and was planning on taking him, but just noticed some tan feathers in his wings. Could feed be causing this ? The pullet I bought is showing no tan feathering.

 

[hdowden]

corn can cause yellowing also sun can bleach the the feathers turning them yellow