New Blue. I agree with teacake-- "noble and stately." I used to use Big Blue. I miss its unabashed garishness, now and then.
Aww sorry, I was just being silly and playing around. There's not actually a purple theme available right now; I simply took a screenshot and played with the colors. I can be slightly terrible sometimes.
Are you using Firefox? If so, use this to change the colors of the site: https://addons.mozilla.org/en-us/firefox/addon/color-that-site/ I'm sure Chrome has something similar as well. It's easily reversible and doesn't affect the way the board operates at all. I use it to create a Halloween theme (candy corn colored - orange, yellow, and white) and a Christmas theme (white, green and red) for TBBS sometimes. I'm also a Lakers fan, so I'll do a purple, gold, and white theme occasionally. It's silly but fun. Oh, and I use Old Grey, since it's easy on the eyes.
I'm using New Blue... but only because I find it the best of three rather boring choices. I'd much prefer a beige or white background with black text for posts, with something more colorful for the page background.
There's a board style chooser?! WTF, live and learn! Gray for me it is, then. New Blue is classiest, but it does get hard on the eyes. Dark brown text on a papyrus background would be ideal... I may have to play around with that add-on Locutus mentioned... *checks that option out* ... But of course you do.