Jeremy,
You might want to update to the newest version of the theme. It lets you choose pretty much any color in the site from inside WordPress’ customizer. You can set the color of the donation bar, it’s graph, buttons, progress, backgrounds, text color. You even choose the font too if you’d like. It’s also responsive so it will work better on mobile devices too.
It’s also possible in either version to change the background of a specific widget. They each have a unique ID. If you’ll let me know which one you’d like to change, I’d be glad to give you a CSS snippet to do that.
Let me know if I can help,
Bill