Jinn

Kinda what NG said:

Our eyes have three color receptors, and just like the RGB of a computer, we get all of our colors by combining red, blue, and green. If you've ever seen the "Jesus on the Wall" optical illusion, you'll know that after a certain length of time, your rods and cones start to get "saturated" with a given color. So if you stare a dark (black) image for long enough, then look at a light surface.. you'll see that afterimage for a few seconds while your rods and cones re-adjust. When you stare at the purple dots, they saturate your red and blue sensors. When it gets rid of the purple dot, your cones have to adjust back to the true color, but only your green sensors are still unsaturated. So you see green until it adjusts and combines back in blue and red to get grey. The green "dot" is not actually moving, they're just removing the purple dots in sequence and your rods/cones get to adjust over and over.

The second part where the magenta dissapears completely is our brain saying "WTF?" and getting rid of the random noise. It's called the Troxler effect.. found a decent explanation on the 'net:

"Our brain tends to tune out static stimuli in our peripheral vision (which is why our peripheral vision is so sensitive to movement; it's probably a trait that evolved because it allows us to better respond to threats). That's why you have to fixate on the central point in order for it to work. Turning off the magenta dots in sequence enhances the fading effect, because when the magenta dot is turned off you see dark gray in its place (the same color as the background), which also leaves an afterimage (albeit a fainter one)--in light gray--that partly obscures the magenta dot when it appears again."

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