QDos, a hardware issue wouldn't show in a screenshot like his is. I agree with the others in that it's an application that's running.
It's an awful lot of fuss for one pixel, and I'm sorry to differ, but Im of the opinion that graphics drivers do not cause a single pixel, out of a few million, to misbehave.
Could be a transistor fault in the TFT that belongs to a neighbouring pixel, but which affects the one that appears dysfunctional. Could be the dysfunctional one has gone bad intermittently.
Tracking down a hardware fault of this nature is quasi-impossible, and worrying to any degree about a single pixel problem isn't really warranted either.
There are certainly far worse things which could have packed up

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