"Molting is timed to meet various needs. For example, resident temperate-zone birds require more insulating feathers in the winter than in the summer. The number is changed in the process of molting; winter plumage may contain more than half again as many feathers as summer plumage. Since the feathers, which carry the colors of birds, are "dead," a bird cannot totally change its colors without changing its feathers (although its appearance can change substantially just from wear). Therefore a male bird usually molts into his most colorful plumage prior to the breeding season."
Emil Graf, everybody.