An observer perceives bands of colour when visible light separates into its component wavelengths and the human eye distinguishes between different colours.
- The human eye and brain together translate light into colour.
- When sunlight is dispersed by rain and forms a rainbow, an observer will typically distinguish red, orange, yellow, green, blue and violet bands of colour.
- Although a rainbow contains electromagnetic waves with all possible wavelengths between red and violet, some ranges of wavelengths appear more intense to a human observer than others.