Green Flickering on Black Pixels - Macbook Pro 2011 (Auto Graphic Switching)
This is related to the AMD Radeon discrete graphics card. It is a hardware issue.

I noticed it come up when plugging in an external monitor on my 2011 MacBook Pro 15" (as it forces the discrete graphics to be used at that time).

The only band-aid fix I was able to find was to force the use of the Intel integrated graphics over the AMD Radeon graphics card. I found a handy utility called GfxCardStatus to both show you what graphics card is in use, and also toggle the use of the Intel integrated graphics card. The utility is available at http://gfx.io

Unfortunately for me in my case, you can't use the integrated graphics card with an external display attached. But at least it gets rid of the green dots in some cases.