The chances of there being any sort of "hack" in use are so low that it's not even funny.

Did you stop and consider that maybe your video card (or chip, if you have integrated graphics) is the cause of the issue? What about addons? Are you using any of those?

Post your computer specs, and a list of addons you are using.

This sounds suspiciously like what one might get if they were using Scuba's Dangerflash addon with the flash set to a grey color.

EDIT: From Dangerflash's author, regarding DF as a possible cause: "You have to be seriously fucking up or (actually) trying to get DangerFlash to do that."

That pretty much leaves you with bad video card/RAM.