|Lesser Goldfinch. Fallbrook, California. May 4, 2014. Greg Gillson.|
Lesser Goldfinches maintain their bright plumage year-round. American Goldfinches, on the other hand, employ a different molt strategy. The bright yellow male "wild canaries" of summer, molt into a dull buffy non-breeding plumage for the winter. Thus, in winter, Lesser Goldfinches are brighter yellow than American Goldfinches!
More details of the American Goldfinch molt are here.