Actually, Mike, that may be a female, which would look more or less this way all year. American Goldfinches are notoriously late nesters in the east, with the first nests not appearing until late June or early July in most cases; out west, they're somewhat earlier, but still often laying eggs into August.
Doing some digging in the Cornell Birds of North America account, I found that males start their molt into basic plumage (the duller look we see in winter) usually in September or later, once the breeding season is complete.