Thayer's Gull?

Yes, the bird in question was centered in the foreground. I guess I should have clarified that. Those markings you described are my reasoning for thinking it's a Thayer's. My understanding with the back is that color can vary, also the overcast does make it darker. From the research I have done, the wing tips are the most important marker on a Thayer's gull, and I feel like they are too dark, though they do look different than the herring wing tips. Unfortunately I did not notice this bird in the field, just seen in my pictures once home, so I don't have another look at it.