English: A comparison of RGB and CMYK color spaces.

The image demonstrates the difference between the RGB and CMYK color gamuts. The CMYK color gamut is much smaller than the RGB color gamut, thus the CMYK colors look muted. If you were to print the image on a CMYK device (an offset press or maybe even an inkjet printer) the two sides would likely look much more similar, since the combination of cyan, yellow, magenta, and black cannot reproduce the range (gamut) of color that a computer monitor displays.

This is a constant issue for those who work in print production. Clients produce bright and colorful images on their computers and are disappointed to see them look muted in print. (An exception is photo processing. In photo processing, like snapshots or 8x10 glossies, most of the RGB gamut is reproduced.)