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Do Yellow and Blue Make Green?
Everything you knew about color mixing is wrong.
Red, yellow, and blue are the three primary colors, the painter’s building blocks. You can mix every other color out of this trio. At least, that’s what they taught me in art class; combine any two primaries, and you get a “secondary” color, which lies between the primaries on the color wheel.
Then I picked up an optics textbook, and my world was turned upside down: the true primary colors are red, green, and blue. You can mix any hue out of these three shades of light. That’s how LCD displays work: by building pixels out of tiny sources of red, green, and blue light.
Why is the painter’s color wheel different? The textbook explained that light and pigments combine in opposite ways. Superimpose a blue and red spotlight, and the resulting light will emit blue and red wavelengths. Light mixes “additively.” By contrast, mixing paints is subtractive. A patch of red pigment is red because it absorbs light of all wavelengths except the red ones. And if you combine red and blue pigment, the mixture will absorb everything that either pigment absorbs. A pigment is a trap for particular wavelengths of…
