I had eaten lunch at a nearby Mexican Restaurant (Los Abuelos) and needed to use the men’s room. I was sitting there browsing on my iPhone (as you do) when I looked up. To my surprise my eyes briefly had difficulty focusing on the green tiled wall. After a second or two I realized what was going on: the tiles were in fact flat. But they were made of glass with a green background, which made them seem to be recessed. My eyes apparently had difficulty figuring out whether I was looking at a flat or recessed set of tiles and tried to switch between. It was a little unnerving.
Taken with an iPhone SE II