Often you will hear a printer call your very colorful print job a “four-color process” job. But there are many more than four colors needed. How does that work?
The four colors used in four-color process printing are cyan (blue), magenta (red), yellow, and black, and is the process often referred to as CMYK, with K representing black, which is used as the key to line up all the other colors.
The inks used are translucent. Layering them allows for creation of a range of colors using basic color principles. Cyan and yellow can produce shades of green; magenta and blue produce shades of purple; and magenta and yellow produce shades of orange. Black could be produced by combining the three other colors, but the result could be muddy and the amount of ink needed prohibitive. The addition of the black allows for cleaner lines, as less ink takes less time to dry, reducing the risk of blurring.
Because the inks are being applied mechanically, there needs to be a way to control the saturation of color to produce lighter or darker tones of color. This is achieved by the halftone process. Tiny dots of color are placed close together, with bits of white from the paper showing between. The eye will perceive the dots as a solid color, but as a lighter tone due to the white showing through. The halftone process expands the range of colors produced greatly.