There is one book I know of which uses text color significantly: Michael Ende's _The Neverending Story_. It's very coarse-grained- the color just tells you whet

There is one book I know of which uses text color significantly: Michael Ende's _The Neverending Story_. It's very coarse-grained- the color just tells you whether currently-described events are in Fantastica or The Human World- and I don't know if it actually assists in reading comprehension or anything like that, but it is a joy to read. As a personal note, the first time I read it, I didn't realize that the colors were significant for a couple of chapters because, for some reason, I occasionally perceive black text on paper as being red, and thus it took me a while to realize that this text actually was printed in red.