A baby bird with an orange beak, beige chest, brown head and wings, and a black tail with white spots on it is probably a spotted towee. This bird can be found throughout much of the Pacific Northwest, including in and around Seattle.
I wish I could answer this! I just saw a bird on my feeder with black wings and back, white underbelly, and an orange chest patch. I can't find it online anywhere!! I wonder if this is the same type of bird you saw. It was in central MA.