The Muser
Physics & Physiology of Color

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The Muser

The Color Musings
Additive Mixture
Subtractive Mixture
Complementary Colors
Primary Colors
Hue, Value, Chroma
Predicting Color Mixtures
Young's 3-color Theory
A 3-color System
Land's 2-color System
James Clerk Maxwell
Thomas Young
Hermann von Helmholtz
Edwin H. Land

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What Are Complementary Colors?
Notice how this word is spelled. The root word is the same as for the word "complete." A pair of colors which can be additively combined to produce white light are called complementary colors, because together they complete the spectrum.

The blue we use as an additive primary color contains light from one-third of the spectrum. Yellow contains the light from the remaining two-thirds of the spectrum (red+green). When blue and yellow light are added together, they produce white light. So one pair of complementary colors is blue and yellow. Another pair is green and magenta. Another is red and cyan.

When complementary colors are combined subtractively, in equal amounts, they produce neutral grey colors, or black.

If a medium-value, medium-chroma red ink is printed over a medium-value, medium-chroma cyan ink, the result will be a grey.

Now, Look again at the color wheel. You'll see that the complementary color pairs are directly opposite each other on the wheel. That relationship holds true for other colors than the ones shown. For example, orange lies between red and yellow on the color wheel. It's complement would be a cyan-blue color on the opposite side of the wheel. The complement to a green-cyan color would be a magenta-red color.

Here we go again. Your first grade teacher probably told you red and green were complementary. They aren't. There's no red color of light that can be added to any green light to produce white light. And there's no red paint that can be mixed with any green paint to produce a neutral grey. Try it—if your red and green paint colors are pure enough, you may be able to mix a black, but you can't mix grey. You'll get a dark brown. If you dilute the paints, or tint them with white, you'll get lighter browns, but you won't produce grey.

Many people think complementary colors are so called because they look well together. Complementary colors are often combined to produce a pleasing effect. But they're called complementary because they complete the spectrum.

Follow this link to a mind-blowing color effect that demonstrates a fascinating property of complementary colors.

© J. C. Adamson, 1997