Color vision is due to a visual system that consists of three different classes of cones.
Each cone contains a different pigment, and each pigment has a different spectral response curve. The three spectral response curves for each pigment overlap across the visible spectrum. Each spectral response curve is shifted with respect to the other along the wavelength continuum so that each has a different maximum sensitivity. The color receptors are commonly referred to as the red, green, and blue cones. The designations refer to the wavelengths associated with each cone system.