Optical illusions involving color.
Illusion 1: A checkerboard with blue and yellow squares, but if you move away from it, you see white.
Illusion 2
Mode 1: A disk with red and green, but when you spin it, it becomes yellow.
Mode 2: A disk with red and cyan, but when you spin it, it disappears.
Illusion 3: A rainbow of colors, but when you pause it from flickering, you only see red, green, and blue.
If Illusion 2 Mode 2 doesn't work, change the background from 255 to between 128 and 135.
If any of the other illusions don't work, try doing them on a different screen.