Make your mind see colours where there are none. Seriously. If you stare at a negative version of an image for a while, which then becomes black & white, you will see it in colour until your eyes refocus.
Hmm, I'm making a pretty bad job of explaining it. Here, try it yourself:
Sweet, huh? To see a bigger version, go Here. You can create one with any photo you find or have on your computer.