I'm impressed that the colours are still so vibrant, based on the photos from the books. Some extra context around restoration of of the book would help.
A book's illustrations don't have that problem, and the pages aren't exposed to the air or sun as much either, if kept on a shelf in a dry place most of the time.
Does make me wonder how expensive the blue pages were to make though:
The fact that only one copy was made suggests it wasn't really intended as a mass-produced book, but as an individual item, perhaps to show to visitors or clients.