The Muser
Physics & Physiology of Color

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The Color Musings
Additive Mixture
Subtractive Mixture
Complementary Colors
Primary Colors
Hue, Value, Chroma
Predicting Color Mixtures
Mind-Blower
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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Subtractive Color Mixture
 

Subtractive color mixture is just like additive mixture in the way that colors of light interact, and stimulate our vision. Almost all practical usage of color involves subtractive mixture. Painting, printing, photography, and fabric dying are examples.

Subtractive mixture starts with the presence of all colors of light, usually as white light reflected from a white surface, such as a piece of paper. Then dyes, inks, or filters are used to subtract some of the reflected light. 

The key to understanding subtractive mixture lies in understanding how colors of light are subtracted. If we put yellow paint or ink on a white piece of paper, it seems like we're adding color to the paper. But the color is already there; the white paper reflects all colors of light, approximately equally. The yellow ink, however, reflects only red and green light. It absorbs blue light, thereby subtracting it from the white light.

Any color of ink, dye or paint subtracts its complementary color of light. Cyan ink on white paper absorbs red light, and allows green and blue to be reflected.

Magenta ink subtracts green light, and allows red and blue to reflect. Yellow ink absorbs blue light, allowing red and green to reflect.

Cyan, magenta and yellow are often used as the subtractive primary colors. Combined in pairs, they produce the colors red, green and blue. When all three primary colors are subtractively combined, they subtract all colors of light, leaving black.

When two of the primary colors are overlaid, they each subtract one color, allowing only the third color to be reflected. For example, if magenta and yellow ink are overprinted on white paper, the magenta ink absorbs green light. The yellow ink subtracts blue light. Neither of them absorbs red light, so the red light is reflected by the white paper, and a viewer sees the color red. 

So, the colors we experience in subtractive color mixture are created in the same way they're created with additive mixture. A combination of red and green light (where the red and green colors each contain light from one-third of the spectrum) will always produce a yellow-colored light (containing light from two-thirds of the spectrum). It doesn't matter whether we started with white light and subtracted one-third of the spectrum, or started with no light (black) and added two thirds of the spectrum.

Similarly, green and blue light always combine to produce cyan-colored light, and red and blue light always combine to produce magenta-colored light.

And complementary colors work in similar ways for both additive and subtractive mixture. In additive mixture for example, yellow and blue light combine to complete the spectrum, producing white light. In subtractive mixture, though, yellow and blue produce black. Yellow ink subtracts one-third of the spectral light, blue ink subtracts the other two-thirds of the light, and nothing is left. No light is blackness. 

Can color mixtures be predicted? You bet.