Underside of right and topside of left.

Noticed this bird on the bay side of Duxbury Beach with other gulls. Out of the corner of my eye I caught a flash of white in the wing and thought maybe I had a first-of-year Bonaparte's before I actually looked at the bird. These photos show the white evident on both on the top and underside of the wing unlike the left which shows the black at the tip on both sides.