The color gamut of a device (computer monitor, printer, scanner, or digital camera) is the range of colors that it can handle. Monitors, scanners, and digital cameras tend to have wider gamuts, as they use an rgb additive color model. Printers must use subtractive cmyk inks to produce colors, which are inherently more limited.

Even computer monitors cannot display every color the eye can see. If just the green phosphor is illuminated, it emits a range of "green" wavelengths of light, some of which stimulate the blue and red cones in the eye slightly. Therefore the green we see on the screen is not the purest possible green we can perceive. To create such a color on a monitor would require introducing theoretical negative blue and red phosphor values, which would mean the monitor would have to absorb some non-green light out of the room. This is not physically possible (yet), nor is it particularly desirable.