Why do some books have colors on the edges of the pages? On some books, I've noticed that they have colors on the edges of the pages. For instance, on my Tikkun): : ![g'mara]( What is the point of these colors? Are they only found on religious books?

This is actually fairly common and has no real significance. It's a purely decorative process called edge painting (or fore-edge painting) because it's color painted on the fore-edge of the book (go figure).

It's common on religious texts, but that's only because religious texts simply tend to be better made and better decorated. It's quite general, though.