For the spotmouth.com site, I started by writing a new theme, but in the end, decided to just edit the acquia theme. One issue that I had was that this theme uses some background images. While I could (and initially did) just edit the images to match the color scheme for my design, it didn't feel right.
I wanted to way a way in CSS to remove the background-image that the theme was setting. I added the following to my local.css and VOILA, it worked: