回答“What is this stain inside my display?”I used to have the same water stain on my Thunderbolt Display. It was huge. Today I just realized that the stain (that was clearly visible) is gone. Can’t tell how it went away. My guess is that my screen saver did not start one night and the display was on for a full 12 hours on a white web page. Maybe that’s what repaired it. Anyway.