It can easially be undone by displaying the same color over the entire screen for a while.

Interesting - I went to the auction of stuff from the Greenwich Milennium Dome and was put off the "C" graded plasma screens because they had severe burn-in - they had been used for information and you could clearly read the words that had been on the screen and see various logos. I took a few flash photos and they showed it up very well.

In the end they weren't sold because they were kept back to be sold with the dome itself. As far as I know they are still in a container at the site - pity because they are now worth a heck of a lot less than 18 months ago (like half).

Gareth