About spot and process color types
You can designate colors as either spot or process color types, which correspond to the two main ink types used in commercial printing. In the Swatches palette, you can identify the color type of a color using icons that appear next to the name of the color.
A 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 combination of the ink as mixed by the commercial printer and the paper it’s printed on, so it isn’t affected by 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 Illustrator.
Minimize the number of spot colors you use. Each spot color you create will generate an additional spot color printing plate for a printing press, increasing your printing costs. If you think you might require more than four colors, consider printing your document using process colors.
A 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, such as when printing color photographs.
Keep the following guidelines in mind when specifying a process color:
- For best results in a 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, those color values will be converted to CMYK when you print color separations. These conversions will work differently if you turn on color management; they’ll be affected by the profiles you’ve specified.
- Don’t specify a process color based on how it looks on your monitor unless 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 a typical monitor.
Using spot and process colors together
Sometimes it’s practical to print process and spot inks on 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.
Important: If an object contains spot colors and overlaps another object containing transparency features, undesirable results may occur when exporting to EPS format or creating color separations. To prevent problems you should convert spot colors to process colors before attempting to export the file or create color separations.
Comparing global and non-global process colors
Illustrator lets you specify a process color as either global or non global. Global process colors remain linked to a swatch in the Swatches palette, so that if you modify the swatch of a global process color, all objects using that color are updated. Global process colors make it easier to modify color schemes without locating and adjusting each individual object. This is especially useful in standardized, production-oriented documents such as magazines.
Non-global process colors do not automatically update throughout the document when the color is edited. Process colors are non-global by default; a non-global process color can be changed to a global process color using the Swatch Options dialog box.
Global and non-global process colors only affect how a particular color is applied to objects, never how colors separate or behave when you move them between applications.