We perceive electromagnetic waves in a small range of wavelengths as light. Different wavelengths are perceived as different colors. Color is therefore a highly perceptual phenomena and depends on the observer and the conditions in which the color is observed (our eye-brain is very accomodating in adjusting for varying environmental conditions). Light with a wavelength of around 7000 (2/100,000 of an inch) is perceived as red and light around 4000 (1/100,000 of an inch) as violet.
