The Lilac Chaser

The Lilac Chaser (also known Pac-Man :p), invented by Jeremy Hinton, is another optical illusion. Quite old, but still pretty nice. Just focus on the cross in the middle.

On the beginning you will see 11 pink (lilac) points on a gray background. There is also a gap which moves every tenth of a second (0.1s) in the clockwise direction.

After a while, the gap will take the green color. This is due to an interesting effect in which the colors of the lilac points are inverted in the optical illusion to a green color. See the image below, that green is right opposite to pink. If the points were black, one would see white where the gaps were.



And in the end, while still focusing on the cross, the points will disapper and you will see just the grey background.
An interactive version of the illusion may be found here: http://www.michaelbach.de/ot/col_lilacChaser/index.html. This version allows viewers to adjust the color, saturation, and timing of the disks.