Sounds more like the LCD suffered some sort of physical shock (even dropping the phone a few inches, if you do it just right is enough, or thermally shocking it), to turn the display into a Liquid Non-crystalline Display. IOW, bad screen. You COULD cause the same thing to happen with software, like the GPU, but the odds are overwhelmingly in favor of a bad screen. (To be sure you'd have to actually test it - connect a known-good screen to your phone and see what happens, and connect your screen to a known-good phone and see what happens.)