Exploratorium
Colorfest

An extravaganza celebrating
the art and science of color

July 1–September 5, 2011

Try This!

Find Complementary Colors in Afterimages
Stare at the dot in the middle of the red flower for 20 to 30 seconds. Then immediately look at the dot in the middle of the outlined flower. What color do you see?

What’s going on?
The ghostly color you see in the outlined flower is called an afterimage. An afterimage is an image that you perceive after you have stopped looking at some stimulus—in this case, the red flower.

When you stare at the red flower, your eyes become adapted to that particular color. Then, when you suddenly look at the outlined flower (which is reflecting white light to your eyes), your eyes don’t respond as strongly to the red component of the light, so you see white light minus red light, which is cyan (blue-green) light. Cyan is the complement of red.

You can try this yourself with shapes cut from colored paper. (If you draw an outline of the shape on white paper, you’ll get a crisper afterimage.) Or stare at any colored object and then look at a white surface to see its complementary color.

flowers