4 –color process uses the basic CMYK colors and is used for those designs that are made of more colors than possible to print on standard machines. This process is similar to how newspapers are printed. Being that this process uses only 4 colors/screens, colors tend to be more dull than simulated full-color process. However, 4-color process is a great option for printing designs such as event sponsor logos that differ drastically in color from logo to logo.
For graphics that have many colors or are of photo realistic quality, you can use either a simulated full color process or a 4-color process. These are more advanced techniques that use halftones of a few ink colors to represent the many colors in the original design. 
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