This document discusses color and color perception. It explains that color is the visual property corresponding to categories like red, blue, etc., derived from the spectrum of light interacting with the eye. The document then provides the wavelength ranges for colors in the visible light spectrum. It describes how objects reflect or absorb different wavelengths, which determine the color perceived. Cones in the retina detect light wavelengths and send signals to the brain to perceive color. The document notes common uses of color in signs, with red indicating danger and green indicating safety instructions. It emphasizes the importance of adequate color contrast in human factors engineering for visibility, identification, aesthetics, and avoiding stress or fatigue.