Colour is not a property of electromagnetic radiation, but a feature of visual perception by an observer.
- The human eye and so human visual perception are tuned to the visible spectrum and so to spectral colours between red and violet.
- There are no properties of electromagnetic radiation that distinguish visible light from other parts of the electromagnetic spectrum.
- Objects appear to be different colours to an observer depending on the wavelengths, frequencies and amplitude of visible light at the moment it strikes the retina at the back of the eye.