Here are some shots of the possible Baltic gull. It was clearly darker than the other LBBs on site and avoided their presence. It was noticeably smaller with little or no contrast between it's back. wings and primaries. I didn't manage a clear shot of the wings, only partial views whilst it was flapping about preening. The bird was also seen by several others including the warden of the Sandwich Bay Bird Observatory.
All the shots are "as taken" with no adjustment to temperature or exposure.
This is about the best shot of the wings I managed.
More shots are on my Flickr site and blog (Greater Kent Birder).