All color management systems share the same fundamental approach, using the same three basic components, a reference color space, device profiles, and a color matching engine. The problem with RGB and CMYK values is that they don't relate directly to our human experience of color. If we want to keep the color consistent, we must change the RGB or CMYK values as they go from device to device. To do that, we need a way to specify color unambiguously, without reference to the vagaries of the device in question. This is the role of the reference color space, often called the profile connection space (PCS).

Reference color space. Unlike the device-specific RGB and CMYK color spaces, reference color spaces represent color in absolute terms: hence, they are often called device-independent color spaces. Virtually all the color management systems in use today, including Apple's ColorSync, Microsoft's Windows ICM 2.0 and Kodak's KICC, use a reference color space based on pioneering work done in the early 1930s by the Commission International de l'Éclairage (CIE), the international body charged with setting standards for illumination

The CIE carried out a large number of experiments in which it asked human subjects to match colors under rigorously-controlled lighting and viewing conditions. The result, based on a statistical analysis of the responses of the experimental subjects, was a family of mathematical models that describe color, not in terms of the ingredients devices use to produce it, but instead in terms of three purely synthetic primary constituents that describe normal human color vision. This family of color spaces based on color as we experience it is known as the CIE color models. CIE LAB is commonly used as a profile connection space, while CIE XYZ and CIE xyY are frequently used for taking color measurements.

Device profiles. To know what color is represented by a set of RGB or CMYK values, we must know the behavior of the device with which these values are associated. To do so, we can take ambiguous device-specific RGB or CMYK values, send them to the device in question, and measure the color that they produce using a spectrophotometer or colorimeter. In the case of input devices such as scanners or digital cameras, we can take a target that contains known CIE color values, scan it, and note the RGB values it produces.

A device profile is essentially a lookup table that records the equivalent CIE values for the RGB or CMYK values used by the device in question. It allows the color management system to attach an unambiguous device-independent color meaning to RGB or CMYK values.

Color matching engine. The color matching engine is the part of the system that does the actual work of adjusting the device-specific values that get sent to the various different devices, thereby keeping the color consistent from device to device. To apply color matching to an image or a color graphic, you must tell the color management system where the image came from, and where you want it to go. You do this by specifying a source profile, usually either the device profile for the scanner on which the image was scanned, or for the monitor on which it was corrected, and a target profile, which is the device profile for the device to which you're sending the image.

The color matching engine then looks at the source profile, determines the absolute color values represented by the device-specific RGB or CMYK, and recalculates those device-specific values to the new ones needed by the target device, as specified by the target profile.

The color matching engine can perform one more useful function-gamut simulation. A device with a wide gamut, such as a color monitor or desktop color composite printer, can simulate the behavior of a device with a narrower one such as a printing press. You can use the monitor as a "soft proof," where you can view a reasonably faithful simulation of the press output, or use a dye-sublimation print as an inexpensive alternative to a color key or a laminated proof.