How Your Eyes Cheat

Your retina has three types of cone cells: one tuned to red wavelengths, one to green, and one to blue. Every color you see is your brain mixing these three signals. When red and green cones fire together, you see yellow. When green and blue fire, you see cyan. These mixed colors still match real wavelengths — yellow light at 580 nm truly exists. But when the red and blue cones fire with no green, your brain hits a paradox. Red and blue sit at opposite ends of the spectrum, with no single wavelength between them. Its solution is to invent a bridging color: magenta.