First up, what do you see in this b&w picture?

Also:
Ladies and gentlemen, I give you... the McCollough Effect:
http://research.lumeta.com/ches/me/possibly the best and creepiest illusion ever.
In short, looking at alternating vertical black and <color> bars and horizontal black and <complement of first color> bars can affect the way you perceive black and white bars for a really long time.
WARNING: This isn't just an afterimage, that's why I didn't include pictures here. It somehow affects your visual systems/memory at a higher level. If you're an artist or something you might want to avoid this. For a web demo like this the results should only last a few hours or a day, but in the original study, some of the participants were affected for weeks or months afterwards.
Hehehe. This one should have you going 'huh' for a while.
What do you se at first? Take a closer look and you will see much more.