Can a book be a mix of color pages and black & white pages?
Of course. However, the full color rate will apply to the entire book in such a case.
The reason is that when we send a job to print we have to select a print profile. That profile tells the presses how to treat the pages in the document … paper stocks, weights, etc. The profile also tells the press whether the covers and interior pages are full color or black and white only. So even if you have only one full color page and twenty three black and white pages, the entire job must be sent as “full color”.