This illusion is great because it makes a succinct argument why the trichromatic theory alone cannot explain color perception (the trichromatic theory says our eyes have three types of color receptors, and that the response of each is directly related to a stimulus's proximity to its preferred wavelength). In essence, this illusion draws attention to the fact that the psychological experience of seeing different colors isn't purely an additive process (like mixing paint). Were that the case, the purple dots wouldn't eventually disappear.
Trichromatic theory isn't wrong, but it's incomplete. It's true our eyes have three types of color receptors, and they do in fact respond preferentially to short, medium, and long wavelengths of light. However, immediately after a receptor is activated, its signal is subtracted from its neighbors. This mathematical derivative helps our brain decipher complex color patterns and distinguish shades of color beyond pure red, green, and blue.
In the case of this particular illusion, our eyes have cells that perform math on red and green stimuli. A collection of cells fire like crazy when there's lots of red and little green(R+G-) and others when there's lots of green and no red(G+R-). When the red dots temporarily disappear in this illusion, R+G- cells shut up, and our G+R- cells cease to be inhibited. As a result, for a brief moment the eye tells the brain that it's seeing green. A similar phenomenon is witnessed when one sees the "green flash" immediately after the sun sets (but only if you've stared at the setting sun sufficiently long beforehand).
Why do the red dots eventually disappear? My theory is that the brain realizes it's receiving a spike in G+R- without actual green stimulation and detects a ruse. The red dots sporadically, but only temporarily, re-appear as your eyes shift and different receptors re-affirm that the dots are in fact real. This leads to the subject of photoreceptor fatigue, but that's a topic for another illusion.
I have plenty of these. I think I'll post more soon.
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