Color is often thought to be a quality of light but this is not so. For example, the expression the ocean is blue uses a perceptual experience of blueness to describe the physical light. Color itself is not in the light. Color is a perceptual phenomenon determined by neural processes in the brain. The region of the electromagnetic spectrum that is visible to humans is from about 400 nm to 700 nm, but no wavelength is endowed with a color. Instead, a particular wavelength, say a wavelength near 470 nm or 580 nm, is perceived as blue or yellow, respectively, only because these wavelengths stimulate the photoreceptors in the human eye that are responsible for the transduction of physical light into neural responses. Those neural responses go through a series of processing stages in the brain. The experience of blue or yellow, as well as all other colors, is a mental construction. The experience of a color is like the understanding of language. There is no meaning in the physical sound (the brain must interpret it) just as there is no blue or yellow in the wavelengths of light. Color is a percept that humans are able to experience through sensory neural processes.
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