Which of the following is NOT a primary color of light?

• A. Magenta
• B. Red
• C. Green
• D. Blue

Answer: (A)

Light combines through additive mixing, so the colors you start with are the primaries of light: red, green, and blue. Magenta isn’t one of these primaries because it isn’t produced by a single wavelength of light. It’s what you get when red and blue light are combined. In the additive system, magenta is a secondary color, not a primary, and it sits alongside a spectrum of colors produced by mixing the primaries. When all three primaries are mixed, you get white; red plus green gives yellow; green plus blue gives cyan; red plus blue gives magenta. So magenta isn’t a primary color of light because it arises from combining two primaries rather than standing as an independent, fundamental light color.