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Color gamuts
A gamut is the range of colors that a color system can display or print. The spectrum of colors seen by the human eye is wider than the gamut available in any color model.
Among the color models used in Photoshop, L*a*b has the largest gamut, encompassing all colors in the RGB and CMYK gamuts. [...]

A color mode determines the color model used to display and print images and color correction. Photoshop bases its color modes on established models for describing and reproducing color. Common models include HSB (hue, saturation, brightness); RGB color (red, green, blue); CMYK (cyan, magenta, yellow, black); and CIE L*a*b*. Photoshop also includes modes for specialized [...]