Spot colors refer to the the pure colors that are not created from screen or dot. Refering to 18 unaltered colors, this is the foundation for further combining for a wider variety of colors.
When on a budget spot colors are useful in cutting corners while still getting a decent product. When needing to recreate a specif made premixed inks are printed using a single printed plate or screen. The Patone matching system is used to assure compatible shades and tints of particular colors. A specif number is given that is used through out the whole matching system to locate a specific color. Useful with printing to convey the proper color and ensure the best possible precision using swatch charts.
Process color uses CMYK and is used most commonly when printing. With an illusion of continuous color what is actual the 4 colors produced at different angles. When investigating closely a dot pattern emerges. However, in spot colors a continuous color is produced all the way.
A cheaper price has always been a big plus for spot colors. Many companies may use a variant of both process and spot color printing methods to assure a reasonable budget. Spot colors also produce much more vibrant colors due to the continuous flow of one tone to produce a unique color. It is used with printing jobs that do not require an excessive array of very different colors. Business cards, monotone (duatone) publications such as book with black text is best executed with spot coloring.
Spot coloring though vibrant has a much more limited color variety than CMYK. Since CMYK images are produced with a variation of each of the colors mixed together the possibilities are much greater. Images that require a variety of color such as photography is inefficient with spot coloring that produces single plates of color at a time.
Spot coloring is a unique option for those producing any form of printed work. Depending on the use it can either be an effective choice, or a terrible mistake.