Why is blue light plus yellow light equal white light, but blue and yellow paints mix to green? Why do the color wheels from various systems use different primaries?
Yellow and blue light mix together via additive color mixing to make white light since the yellow light is missing blue wavelengths that are filled in by the added blue light. Subtractive mixing of yellow (which removes the blue light) and cyan (which removes the red light) results in green. A subtractive mixture of a true yellow (removes blue) and blue (removes red and green) would result in black. The term “primary” is used differently in different systems. For example, Munsell and NCS don’t actually use the term at all. Munsell has principle hues and NCS uses the unique hues. Since primary can mean different things in different systems, the term needs to be interpreted carefully. The best generic definition is that of a “set of primaries” such that no one of the primaries can be made by mixing the other two.
Related Questions
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