This is a photo of a recentish book taken while backlit from a window. Notice that the pages have a slight yellow tinge to them, what I would call paper white. However you can see that the pages look very blue along the spine. This is not a photographic artifact, it is even more noticeable to the eye.
Can anyone explain why this would happen? I assume that the paper bleaching process might add some UV dies, but that seems to be something that would effect the whole page. Why does the color change just in this area?
UPDATE: the sunlight is from BEHIND the camera. The blue color is due to reflection not transmission. The outside of the book is very light grey. This effect happens with any book, go try it yourself.