Once the fall (non-breeding) season gets here, the plumage changes to the more drab, boring colors, that in many cases make identification a little more challenging.
Here is the spring (breeding) plumage
And here is what they look like now.
Just to show the difference, here is a Franklin's Gull, in spring plumage. The biggest identifier is the much broader eye arcs, where the Franklin's are thinner.