For a good printing result, knowing the difference between Spot Color and Process Color is really essential. Also, choosing properly between spot and process color will affect the final costs of the whole printing process as well.
If you are a print designer, it’s your responsibility to get the best result for your (clients) business cards, brochures, stationary or other print designs. The most important phase in this process is pre-press production, including converting to the proper CMYK color model, finalizing the files, etc., etc.
As you probably all know, there are several color models: RGB, CMYK, LAB etc. The 2 most common used color models are: CMYK (subtractive color, used for printing and based on inks use), and RGB (additive color model used for computer displays and based on light transmission).
This means that the artwork you produce either has to be spot color artwork or CMYK artwork, so please, .. never use RGB artwork for print design! In Illustrator (or InDesign) you can assign colors as either spot or process color types, which are the two main ink types used in commercial printing.
Read how to use Pantone colors to create spot-color documents  in the Swatches panel of Illustrator and/or InDesign. In this article I hope to show you which color option is best for your print design, and also why.
Process Color (CMYK)
Process color printing, also known as CMYK or four-color process printing, is a method that reproduces finished full-color artwork and photographs. Process colors are being used when a job requires so many colors that using individual spot inks would be too expensive or impractical.
Artwork and photos are reproduced when the colors in the artwork are separated, then halftoned (converted to dots). Process colors are reproduced by overlapping and printing halftones to simulate a large number of colors.
CMYK offset printing includes using 4 printing plates for each separate color: Cyan, Magenta, Yellow and Key (Black). Each print plate, flexible enough for mounting around a cylinder/roll on the press, transfers its image to a rubber blanket that in turn transfers the image to the paper. The plate itself does not actually touch the paper — thus the term “offset” lithography.
Offset printing is one of the most common ways of creating printed matter. Compared to other printing methods, offset printing is best suited for economically producing large volumes of high quality prints in a manner that requires little maintenance.
Spot colors are printed with premixed inks on a printing press or screen printer. To ensure that a printer uses the exact color that the designer has in mind, the Pantone Matching System (PMS) is used and is highly recommended for corporate or institutional printings.
Each PMS number matches a unique spot color, so you can maintain the same color fastness throughout different print media. Spot color can also be used to refer to non-standard inks, and can vary from pastels to fluorescent and metallic, as well as clear varnish, or anything else that requires its own printing plate.
Spot color printing creates brighter, more vibrant results, but with a smaller color range. Spot color printing would be typically used for jobs which require no full color imagery, such as for business cards and other stationery, or in monotone (or duotone etc) print.
It’s also important to remember that spot colors may not actually translate to matching process colors. Unlike process printing, which prints dots of color, a spot color is printed at 100% and has no dot pattern.
When printing in single (spot) colors, a single color ink is applied to the printing press roller. Each separate spot color is reproduced using a single printing plate, and a single run of the press. If there are two colors, there will be two plates and two runs, and so on. The colors are layered onto the paper one by one.
Important: 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.
Using spot and process colors together
If you’re designing an annual report with one exact company logo color and multi-color graphs, charts and photography on the same page, then it’s practical and advisable to use process and spot inks together in the same job. You can apply the spot color to the logo and process to the other elements of the page.
Remember that this goes to increase your costs because you will get four plates (CMYK) plus a plate for each spot color you may add as result.
Tip: Don’t specify a process or spot 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.