The term gamut refers to the range of colors that can be reproduced by a given process. When considering colors for display either on paper or on a display device, it is important to consider the gamut of that process. Computer monitors can usually produce brighter colors than ink on paper.
Colored inks on paper act to filter out reflected colors. The subtractive primaries (cyan, yellow, and magenta), when combined on a printed page, act to remove colors from the light reflected from them. Yellow ink absorbs blue; magenta ink absorbs green; and cyan ink absorbs red.
In theory, if all three subtractive colors are printed on a page, the result should be black. However, in practice, the combination of these colors does not produce a completely black page. Hence, all quality printing processes use four colors: cyan, magenta, yellow, and black. The black ink is applied to the darkest areas of the page, where the sum of the other three ink colors does not produce a dark enough color.
If you are involved in the production of printed documents, it is important to work with the printer to understand the gamut of their process. Experienced print shops can help you select colors so that the differences between a given color on a display device are as close as possible to the colors printed on the page.