Artists traditionally refer to red, yellow, and blue as primary colors. These three colors were once believed to be the essential set for mixing a broad palette in painting. Following this line of thinking, violet, green and orange become secondary colors because they’re mixed from the primaries.
However, for more than a century, both scientific understanding and practical experience has shown that cyan, magenta, and yellow are more efficient for subtractive mixing with pigments, producing clearer and a more saturated range of colors. That’s why printers use those three primaries, designated as CMY (actually printers use CMY plus black).
Additive primaries
In other artistic and technical fields, there’s another set of primary colors. Red, green, and blue (RGB) serve as additive primaries in digital displays, photography, and theater lighting. If you talk to photographers and lighting designers, they regard yellow as a secondary, achieved by mixing red and green.
The persistence of the red-yellow-blue model in art education is due largely to historical convention rather than optimal color mixing. One of the first things new painters discover is that it’s hard to mix a vibrant purple with those classic grade-school primaries.
I once asked my brother, who taught kindergarten, if we could shift a child's understanding of color, and teach them a different set of primaries than the red-yellow-blue set. If we started them young, maybe kids could learn that all six of those colors are primary: namely yellow, red, magenta, blue, cyan, and green. But he said forget it, that's easier said than done. Colors are far too deeply ingrained culturally.
I’ll admit, it took my brain more than a year to map cyan and magenta as distinct primaries, and not just a kind of blue and a type of red.
What’s a practical solution?
A practical approach is to recognize that “primary colors” are not a universal set given by God or nature, but the set you use, and the way you map the world of color depends on the context and your goals. When the aim is to achieve the widest possible gamut from a set of three starting colors, then cyan, magenta, and yellow for pigment, or red, green, and blue for light, are scientifically preferable.
It doesn’t mean you have to look for pigments that match those printer’s primaries, but rather that you calibrate your eyes and brain to map the world that way.
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