Colors and their opposites, in this Moment of Science, beginning with some thoughts about paint.
We usually think of paint as a substance that adds color to things. But, from a physical point of view, paint works by taking colors away -- from white light.
Take the example of a red car parked in the sun. The sunlight already contains all the colors of the rainbow. The red paint on the car absorbs the non-red colors from sunlight and reflects only red to our eyes. Red paint absorbs, or subtracts, non-red from white.
What happens to those non-red colors absorbed by the paint? Actually, the absorbed light is converted to heat. But here's an almost philosophical question. If we could, somehow, see the light that red paint absorbs, what would we see? That is, what does non-red look like?
In fact, it's a bluish green color called cyan. People who work with color professionally say that cyan is the complement of red.
Cyan is the color that red paint takes away from white light. Now, what if you put cyan and red back together? When you add cyan light to red light you get white light -- you're reassembling the colors of sunlight. Whatever colors aren't supplied by the cyan are supplied by the red.
With paint it's different. Cyan paint added to red paint makes black paint, because whatever colors the cyan doesn't absorb, the red does. Nothing is reflected, so the paint looks black.
The mixture of any color and its complement makes white if you're mixing light, and black if you're mixing paint. This is one of the basic secrets in any business involving color— from painting to color television.
