Yeah the dullness of the individual compared to photos online is what stumped me a bit, but it didn't match anything on the guide and of the unsigned species I'm aware American Redstart was easily the best match.
It looks like an American Redstart to me. The dullness might be related to winter plumage. This species doesn't have a drastic plumage change in the winter, but even a small lightening of the yellow on the sides might make her seem dull.
