One Color and Multi-Color Printing
The majority of books printed in North America are single color (black). There are printers who specialize in color work, both as flat colors (graphs and charts) and full color (CMYK), but much of this work is done offshore (Europe and Asia). File preparation for color printing should be left to an experienced designer.
Single color printing is the same for all books; an image is reproduced on both sides of a sheet of paper. But where a digital printer might image one or two or four pages in a press pass, offset lithographers may print 32 or 64 pages in a single pass.
Books printed with ink instead of toner require a plate for each color and two plates for each full signature, a front plate that prints one side of the sheet and a back plate that prints the other. A 64-page book produced in one color in 32 page signatures would need 2 front plates and 2 back plates, for a total of four plates.
The finished sheet may be 35" wide to as much as 50" wide and require folding or cutting (or both) to become a signature for your book.
Multi-color printing requires a separate plate for each ink color, so the same 64-page book printed in 2 colors would require 4 fronts and 4 backs, or 8 plates. Toner based presses can typically lay down full color in one pass without any plates, although digital inkjet printers can use as many as 6 different color ink cartridges to produce full color.
Because full color book printing requires 4 plates per sheet side, and the plates must reproduce images as small as .0033" in perfect register with each other, it is almost always most efficient to run all four colors on one sheet side in one press pass. Not only can the pressman adjust inking and register by comparing a finished sheet to your approved proof, the stability of the physical dimensions of the paper is assured.
Reproducing full color is labor intensive by highly skilled craftspeople. It is never an inexpensive proposition: the only way to control unit costs (per book costs) is to increase run lengths since there is so much set-up and prep work involved in full color printing.
Unfortunately, that's meant that full color printing is following many skilled manufacturing jobs overseas. At one point, books printed outside of America were not eligible to be covered by United States copyright, but today that's not an issue.
Additional information about printing processes is available at Digital, Sheet-Fed, or Web.