Use process-color printing if you want color photographs in your publication.
In process-color printing, all the elements on a page are separated into percentages of four colors and printed with separate press plates:
Printers use process-color printing to print full-color photographic images. Process-color printing uses four translucent inks: cyan (C), magenta (M), yellow (Y), and black (K), referred to as CMYK, to create a wide range of colors. The CMYK color model produces a range, or gamut, of colors that are sufficient for most printing needs. Theoretically, combinations of cyan, magenta, and yellow can be combined to create all these colors, including black.
However, imperfections in the CMY inks cause a deficiency in darker tones and in creating a true black. To correct this, printers use translucent black ink (K) to darken shadow areas and to create opaque black. However, because the black ink is translucent, it is insufficient on its own to create a fully-saturated, opaque black. In many cases, printers will boost the black ink by combining it with one or more of the CMY inks to create what is called rich black. Combinations of black tints and other inks are also used to create gray tones that can't otherwise be created with a black tint alone.
Process-color printing is more expensive than spot-color printing and involves more work for the printer. However, if you want color photographs in your publication, this is the type of printing you need to use.
Finally, let's look at process-color plus spot-color printing.