"Our grasp on color becomes more tenuous still when we try to recall it by memory"

“What if, when we talk about the color red, we all see a different color and no one knows?” is grade-A amateur philosophizing that is usually followed by head-scratching. But it is a question that has commanded the serious attention of scientists: How do humans see and understand color?

Scientists estimate that the average human can perceive a mil- lion different colors. We have the ability to do so because our eyes have three types of specialized cells—called cones—that are predominantly clustered in a tiny patch on the retina. When wavelengths of light hit the retina, these cones decipher the varying lengths and help translate them into identifiable colors in the visual cortex of the brain. Along the way, our brains factor in numerous variables that could affect this interpret...