I remember when I saw my first goldfinch in winter plumage. I thought I had a rare bird that dropped by the feeder. I e-mailed the Stokes, who kindly visited my photo and told me it was a goldfinch! The goldfinch then, in 2007, was only partially in winter clothing. The ones that visited us in December were wearing all of their brown feathers.
Goldfinches don't come often to the feeder. They come in small groups when they appear. They are quiet and mingle well with the other birds. If you don't watch carefully, you could confuse them with sparrows or redpolls.