Thanks to some poking by Wimpie, I've added a few themes to the forum, that you can select in your own profile's "Look and Layout" option. The default is Chocolate Curvaceous, but there are a few others, like Ambassador2.0 as used on M&F's forum, or AlphaCentauri if you like a starry background and white post backgrounds (I'm using that now, fwiw.)
If you would like to make some suggestions, you can find a large list of SMF themes available here:
http://custom.simplemachines.org/themes/I'll take a look at any suggestions, and unless they break something, add them for your enjoyment.