Glad you find it useful!

is there any way to format the html output so that the text background is transparent and the text itself remains opaque?

Transparency isn't a function of the HTML, it's a function of the web browser - either WebDesktop, or Firefox, or Safari, or whatever. So what you're really looking for is a web browser with a transparent window, ideally WebDesktop with a transparent window.

I'm not sure how to accomplish that, but a quick search turned up a couple of OS X utilities that claim to make your windows transparent. You might experiment with something like CrystalClear Interface or Afloat and see if that gets you closer to what you want.

Good luck!