Like Andrew said. You need to keep in multiples of 4 for book publications. Even if you have to add in blanks.
You want to add pages of photos into the middle of a 32 page book that are colour.
So you are looking at a 16 page section, plus a 4 page section, plus a 8 page section plus another 4 page section. (16 + 4 + 8 + 4 = 32)
You're first 16 will bring you up to half way through the book and onto a left hand page. That's exactly what you want, because 16 is half of 32. Then, facing the left hand page is the right hand page, page 17, where the photos begin. You will have 4 pages of photos then.
Then 17, 18, 19 and 20 are the middle 4 pages. And the rest will work out by itself.
So your text restarts from page 21 - 32, which is 12 pages exactly.
The last section of 8 + 4 may well be printed as a twelve page section or a 16 page section and waste the paper, but that's not really any concern of yours.
Good luck with the book!
Euge