Help me identify this bird!

Live in Northern VA. Saw a bird at my thistle feeder that today that I cannot identify. Sparrow-sized, bright white with dark brown chevron across back of neck and lower down on body, close to tail; yellow legs. First thought was that someone's parakeet had gotten loose! Any ideas? We have thistle feeder, wild bird seed feeders and suet in the yard. Did not check out anything but the thistle. Perched on our fence and was not shying from the sparrows. Thanks.