My comic currently looks like this-http://www.drunkduck.com/Fox_Fire_art_and_concepts/
- while I'm fixing it up, and as the comment says the text is a little hard to read. How would I get the areas in the authors and readers comments to appear in a solid colour to make it more readable?

There are many ways-
*If your content is in tables you can give the tables a background image of your choice -preferably something fairly neutral.
*Again with tables- you can give them a background colour.
*If you're using CSS one of the easiest ways to do it would be to change the properties of the TD tag to include a background colour (because all comments are printed out in tables when the page is rendered.
*Again with CSS you could just add a background colour property to all text, or just text inside table data cells, or whatever. That would be pretty god too.

If you want help doing any one of those things, but not all of them, let me know.

OK, both the author comments and the readers comments look like they're set into tables (I haven't modified anything in that section from the DD raw HTML), so how could I add a background image to them?

OK, with the way your page was structured, the easiest way was to simply add bgcolor="#FFE2A8" into the table data properties of the table cells with the author notes and the user comments. You can change the colour ...
You could use a background image instead, all you need to do is replace the backound colour property with this:
background="http://www.webAdreescom/yourPic.jpg"

Thank you so much! It worked like a charm!