Brown - Same actuation point up and down. Has a tactile bump at the actuation point, but no audible click. Not as strong of a tactile sensation, since there's no moving piece to spring around on the key while traveling.
About halfway down, this page illustrates the different key types and how they work mechanically:
http://lifehacker.com/how-to-choose-the-best-mechanical-keyb...
There's plenty of youtube vids comparing the two, I think this one [1] shows the difference quite well. Both blues and browns feel very similar, but the blues are much louder. Browns are already quite loud, and IMO blues are too loud - especially if you're in the same room as others. I went for browns.
Once you've typed on this thing for some time, there is no going back though (except, maybe MacBook keyboards, which are also superb)
[0] http://www.wasdkeyboards.com/index.php/products/keyboard-acc...