Cones of the human eye
Chapter 7 endnote 2, from Lisa Feldman Barrett.
Some context is:
Our receiver [of light rays] is the human retina, which uses its three types of photoreceptors, called cones, to convert the reflected light into electrical signals made meaningful by a brain. [...] All three cone types must work together to perceive a single category of color, like red
Each of your eyes contains a retina — a layer at the back made of cells that convert light energy into electrical signals, enabling you to see. Your retina has two kinds of light receptors — rods and cones. Most human retinas contain three types of cones, each responsive to short, medium, or long wavelengths. These are mistakenly called blue, green and red cones, respectively. Red cones are not responsible for seeing red light in a one-to-one fashion, and likewise for blue and green cones. All three types are necessary to provide the brain with the information that we categorize as a color. It is a constructionist enterprise with basic ingredients (three different cones). The relative difference in the signals from the three cone types provides the brain with the raw signal for color vision (e.g., to see red, you need all three cone types).