If you only want to print one or two colors on a page, it makes no sense to use the four-color CMYK process. Instead, printers mix inks according to formulas to produce specific colors. The formulas are developed by ink manufacturers and by independent graphics companies.
Spot colors are selected from books or charts that contain printed color samples, each of which is identified by some number. Usually, the numbered colors are also described in the CMYK system. One widely used numbering scheme is known as the Pantone® Matching System, or PMS. Professional graphics software packages provide color selection from this and other spot color systems. Spot color inks can also be printed in percentage tones, just like black ink with the greyscale. This gives the designer a wide range of "color" effects for much less than the cost of four-color printing.
Example: One Pantone® color that is very similar to the light tan border above is PMS 148C. In RGB, it is #FBD09D; in CMYK, 1C 20M 41Y 0K; in HSB, H3 S37 B99.
Colors will not look the same on your monitor as they do on a printed page, even if you have a true-color display card and you enter the RGB or CMYK values precisely as given. Professional graphic artists use high-end monitors that have been calibrated to show colors as closely as possible to the printed page—but even then, direct and reflected light just aren't the same thing.
Copyright 1997–2013, Tom Jewett,
tom [at] tomjewett [dot] com
Department of Computer Engineering and Computer Science, Emeritus
California State University, Long Beach