CMYK
CMYK, or process color, is the term for the inks used to add multiple colors to books. Books that use these inks are called four-color books because they use a combination of four colors - cyan, magenta, yellow, and black - to create a design's desired color. Books containing color photography or colorful art will use CMYK when printing. Solid inks can be used in tandem with CMYK to make the color stand out.
Four-color vs two-color
As opposed to the versatility of four-color books, two-color books will not use CMYK and will instead only use black and another solid ink color. These solid ink colors are most commonly Pantone inks. Unfortunately, digital printers do not support Pantone inks, so two-color books cannot be printed using a digital printer. The only ink options for digital printing are CMYK and black.
