Because of a number of device factors, printers represent the most difficult portion of color management. Color is generated in an entirely different way on printer than it is for displays or digital cameras. Typically, the user starts with white paper. The actual spectrum of the white can vary depending on the illumination being used to view the output. In general, the spectrum is broad.
Printers use what is termed a subtractive process.
There are various types of printer technologies such as photographic, thermal, electrostatic and ink-jet. Printers can be strongly affected by the type of paper used, because they have complex surface interactions with the dyes and paper. Whether the printer is continuous tone or needs to be half-toned also makes a large difference. In CRTs, a color profile can be generated with anywhere from a dozen to 140 measurements. Scanners and digital cameras might require up to 200 or so measurements in their color spaces.