As you work with color images and color output devices, you soon realize that there is no standard color monitor, printer, or scanner. A color space is a method for representing the possible output colors for a device by using a hypothetical one- to four-dimensional space. Each dimension in the space represents different intensities of the components that define a color. For example, a common space is RGB (red, green, blue). This three-dimensional color space is defined by using the three primary colors of light. Many other spaces exist that address other specific needs, such as printed color.
Although every monitor you buy is undoubtedly an RGB monitor, the RGB color space it supports varies depending on the quality of the monitor's components. Different phosphors produce slightly different shades of red, green, and blue. Cheap monitors might have a slight yellow or green tint to them, whereas LCD panels have vibrant hues but less consistency in gradations than professional CRT displays.