Illusiontime

Here's a nice illusion:

Stare at the central dot in the image. 

Wait for the image to switch over to the color-inverted version. Keep staring at the dot.

Now, when the image switches back, you should see a 'normally' colored picture (the colors might be a bit washed out).

But! Look around the pic now - it is still a grayscale image!

How I think it works:

The reversed-color image causes specific (spatially congruent) bits of the retina to adapt to the color at that point. So, when the inverted-color image goes off, you get a recovery, which is the true color, and that 'paints' the grayscale :)

(Photo (c) me)