I’ve got a Acer 19″ LCD that’s had a pixel almost dead center show up as green a couple of times. The first time it freaked me out and I started digging for my receipt expecting that I would be sending it back in for replacement. Didn’t find it though. After a couple of hours I got tired of looking at the green dot and touched the pixel. It got a little dimmer. So very gently I tried rubbing my monitor where the green dot was. After a couple of passes it disappeard.
I have no idea why this works, but it has worked the couple of times that the green dot has shown up. Be sure to wash your hand first though. The first time I left a nasty mark on the monitor that had to be cleaned off.