left/right arrows change/reverse spin speed
up/down change size
The spinning image has no colors in it but when rotating at the right speed and size, the dashed lines begin to look like different colors.
This only kinda works on a pc due to refresh rates, etc. But if you print out the sprite at about the size of a cd and spin it (make it into a top, poke a pencil though the middle, etc) you will see the color effect more clearly. Peace - Loco
ps. This and many other optical illusions work basically by short circuiting your brain. Ie.. there are no colors in this disk, but your brain was hacked :P