If your eyes follow the movement of the rotating pink dot, you will only see one color, pink.
However if you stare at the black “+” in the center,
the moving dot turns to green.
Now, concentrate on the black “+” in the center of the picture. After a short period, all the pink dots will slowly disappear, and you will only see a green dot rotating.
I get why the “absence of pink” goes green, but how do the pinky dots disappear?
Rod fatigue?
As I continue looking the pink dots come back, somewhat fainter.
There are loads of optical illusions on this page, including this one, which is identical to the one in the OP. And all of the illusions include very complex explanations of just how your eye or brain is flummoxed to create the illusion. This one is one of my favorites.
I had a girlfriend like that once.
I like this one. If you aren’t an Evangelical Fundamentalist Christian, you will be after this.
This has been a favorite of mine for some time now. (There may be an ad you’ll have to click away. Sorry.)
This is fun stuff. I emailed a couple already to amaze and amuse my friends.
I think I’ve worked it out: the green retinal after-image exactly cancels out the pink of the dot, rendering it gray - the same gray that the makers of the illusion have used for the effect to work. I think.
I’m with *tdn, only it would be cone fatigue, right?
[Cartman]
I see a goddam hippie!
[/Cartman]
This one was awesome. I thought it was a joke until I moved my eyes.
That is very cool indeed.
Great fun. Bookmarked.
*::: Now I’m dizzy . :: *
If you really want to break your brain, try this thing, and example of the McCollough Effect. It’s been a few years since I’ve tried it myself, but I recall the effects lasted at least 24 hours for me.
Hmm… nothing’s happening for me. 
There did seem to me to be a yellowish haze around the horizontal bars already, from the very beginning. Is that supposed to be there, or is my LCD monitor doing something funky maybe?
-FrL-
That is neat. It only works if you keep your eyes really still though… I find the odd pink dot keeps reappearing. Sometimes it looks like the green dot leaves a trail of pink dots behind it as it rotates, which slowly fade. Aren’t our brains weird?
I also see the yellowish haze. It appears on both my lcd and crt screens so thats not it it seems.
LEAD SINGER NAME!
(not really a good band name)