I noted a Dark-eyed Junco at my feeder in Seattle with a partial (throat and malar areas) white collar this morning. It was close enough for me to see white feathers were poking out beneath the dark gray feathers on the neck. I suspect that these white feathers are a downy under layer, and the white "collar" is an effect of molting where new dark feathers have not yet grown all the way over the white layer.