I have a late 2007 iMac a1224 that has developed this pixel in the top right quadrant of the screen that is burnt, dead or something? I can't quite pinpoint the color, sometimes it looks green, other times almost clear.. like some spit? Do you know what I am saying? It only shows up on lighter backgrounds.. black backgrounds don't show it.. I have tried some of the pixel fixers, to no avail.. Any suggestions? What exactly is it?