Thank you for posting this important question. Unfortunately this is a problem that doesn’t have an easy solution. Book collectors are told to learn to live with it. The reason for this is that foxing (those brownish, yellowish, orangish spots on book pages) is very common even in rare books. Foxing is caused by a combination of elements: poor quality paper, damp storage conditions, and a kind of mildew organism. The reason we are told to live with it is that the coloring is embedded in the fibers of the paper. It is not surficial! That means you can't scrape it off because you would scrape a hole right through the page.
It is possible to treat the foxing. Book and Paper Conservators know what chemicals to use. However, in order to use the chemicals on the spots they have to DISBIND the book. They can only remove foxing by taking the book apart and washing and treating the pages individually. You can imagine how expensive this is!
Warning! Trying to do this yourself by treating with bleach (hydrogen peroxide) will damage your book worse in the long run from the acid!
Ultimately, the answer is to find a replacement copy that has no foxing if you can or embrace the book collector ideology and learn to live with it. They are sort of like age spots on your Grandma's hands. No big deal, right?