The best solution would be to put some Javascript links on the page that change the text and background colors when you clicked on them. The downside to this would be that it would revert to default every time you went to a different chapter, though.
That Javascript is something I could reasonably write in ten minutes after I get home from work tonight. I'll do so and post it here unless someone produces a better solution before then.




This should do it. Put a copy of jquery-1.4.2.min.js in the same directory (jQuery is a Javascript library for keeping browser compatibility bugs at bay).
This stores the color scheme in a cookie, so it's preserved when you move between chapters. The setCookie and getCookie functions came from here. Given the example, this should be pretty easy to extend for things like changing text size and margins, if you are so inclined.