How your eyes' receptors (which are sensitive to certain colors) can get tired. When they don't work as usual, you may see an afterimage in colors that are different from the image you were looking at. An afterimage is when your eyes see something that isn't there.
- The image of the yellow and blue flag below
- Stare at the yellow and blue U.S. flag for about 20 seconds.
- Then mouse over the flag image, which will make it disappear.
- What do you see in the white space?