Spot vs Process Colors: pdf

Spot color is a special premixed ink that is used instead of, or in addition to, CMYK process inks, and that requires its own printing plate on a printing press. Use spot color when few colors are specified and color accuracy is critical. Spot color inks can accurately reproduce colors that are outside the gamut of process colors. However, the exact appearance of the printed spot color is determined by a combination of the ink as mixed by the commercial printer and the paper it’s printed on, so it isn’t affected by the color values you specify or by color management. When you specify spot color values, you’re describing the simulated appearance of the color for your monitor and composite printer only (subject to the gamut limitations of those devices).

For best results in printed documents, specify a spot color from a color-matching system supported by your commercial printer. Several color-matching system libraries are included with InDesign.
Keep the number of spot colors you use to a minimum. Each spot color you create will generate an additional spot color printing plate for a printing press, and increase your printing costs. If you think you might need more than four colors, consider printing your document using process colors.

Process color is printed using a combination of four standard process inks: cyan, magenta, yellow, and black (CMYK). Use process colors when a job requires so many colors that using individual spot inks would be expensive or impractical, as when printing color photographs. Keep the following guidelines in mind when specifying a process color:

• For best results in a high-quality printed document, specify process colors using CMYK values printed in process color reference charts, such as those available from a commercial printer.
  The final color values of a process color are its values in CMYK, so if you specify a process color using RGB or LAB, those color values will be converted to CMYK when you print color separations. These conversions work differently when you turn on color management; they are affected by the profiles
  you specify.
  Don’t specify a process color based on how it looks on your monitor, unless you are sure you have set up a color management system properly, and you understand its limitations for previewing color.
  Avoid using process colors in documents intended for online viewing only, because CMYK has a smaller color gamut than that of a typical monitor.

Sometimes it’s practical to use process and spot inks in the same job. For example, you might use one spot ink to print the exact color of a company logo on the same pages of an annual report where photographs are reproduced using process color. You can also use a spot color printing plate to apply a varnish over areas of a process color job. In both cases, your print job would use a total of five inks—four process inks and one spot ink or varnish.

— Adobe InDesign online help