What's cool about this for me is that, even though I'm somewhat red-green color blind, everything this illusion purports to do, happened! I feel 'normal'! Can I learn the secret hand shake now? Huh? Please?
The brain can only do one thing at a time, just like any computer.
By concentrating on one thing, the secondary image becomes background noise, so to speak. Eventually the brain discards the background image so it disappears.
When we first start talking to someone in a crowded place, the background noise makes conversation hard, eventually the brain drops off the background noise and a conversation in a loud place, becomes comparatively easy.
The rotating image is always disappearing and reappearing so the brain still holds that image as the moving image is there at every refresh, but in a different position.
The green dot is there because of the brains automatic color balance response. It's trying to even out the magenta color by making a negative bias on it and when the pink dot disappears the negative image shows up. As you stare long enough the brain sucessfully cancels the magenta colors and you only see the negative color showing when the magenta dot disappears.