Question

Why is visible light arranged into colors in order: red, orange, yellow, gree, blue, indigo, and violet?

Answer 1

Because that part of the electromagnetic spectrum moves from the longest wavelengths (red) to the shortest wavelengths (violet). As the wavelength changes our eyes perceive different wavelengths as different colors. Actually, our eyes see the light, a chemical change takes place, and energy is sent by the optic nerve to the brain which perceives the signal as objects and colors. If you are interested in that aspect of light, look up cis/trans isomerism and how that affects the rhodopsin in the eye.