Peanut hearts, buckwheat and canary seed will do it. This means ordering it from a bird supply company. A secret ingredient of cage-bird feed is the seed of a member of the lowly cabbage and turnip family with the exotic name gold of pleasure. For generations, old hands at Canary breeding used it to gloss up plumage and promote singing. It does the same for wild birds.
Goldfinches color up and sing.
So do Redpolls and Cardinals. Little research has been done on the effect of this seed on wild birds, but there seem to be no harmful results.