Say you need a physical copy of a company logo you designed, so you print it out. You look at your results only to find that the colors are way off than your original logo. If you have ever heard of spot colors, know that this would have obliterated your entire dilemma in a heart beat if you had only used them before.
There are two color types used in printing: a spot color and CMYK. A spot color is a special ink either pure or mixed that is printed in a single run, requiring one printing plate. It does not change from page to page during the print run. Common ink vendors are the Pantone Matching System (in the U.S.) and Tokyo Ink (in Europe). CMYK (Cyan, Magenta, Yellow, and Black) is a color type which achieves a full range of color with printing. Both of these color types are created without screens or dots.
Spot colors are used to maintain the accuracy and consistency of the color you are using throughout the print run. Logos are usually created with spot colors so that it can stay the same no matter who the print vendor is. This is important to make sure that the branding of a company, products, and/or services remains the same when reproducing it.
Make sure you are wise when spending on printing. Each color plate that is used during a price run costs money. It is better to use four-color process inks (CMYK) when printing continuous tone images like a photograph instead of Pantone. If you want a nice ol’ blend of purple and your on a limited budget, use a Pantone color. Spot colors will be cleaner and brighter than if printed in four-color process due to the gamut of the 18 basic colors. The gamut (or color gamut) is a certain complete subset of colors in color reproduction. It is better to use Spot colors when few colors (one, two or three color jobs) are specified and color accuracy is critical. This is why they are commonly used in corporate logos and identity programs.
So now that you know all about spot colors, go ahead and use your new knowledge to print out a logo (or whatever it is you want to print that requires few colors) correctly!