Whoa, hehe, I had a major blonde moment (no offense anyone), I saw it, blinked, and was like, "and....", and then I did it again, and again a third time before it clicked lol. Thats really cool! Nice relief from homework! Thanks bro!
The green dots are called negative afterimages. Green is the complementary colour of pink/purple. If the original dots were green, you would see pink afterimages. Orange dots cause blue negative afterimages and vice versa.
Take a look at the colour wheel of your favourite graphic software. Colour and complmentary colour are opposite of each other on the colour wheel.