What is 4 color printing?

Any company that can provide offset printing services will typically use the 4 color printing process, and this is also true with almost every commercial printer. This color scheme uses 4 standard colors, cyan, magenta, yellow, and black, and it offers printed images that are vibrant and realistic. RGB is a color scheme that only uses 3 colors.

Each color [with CMYK] is represented by a corresponding value of cyan, magenta, yellow and black inks, on a scale from 0% to 100%.

Source: 99Designs.com