big enough for life's necessities: 2 little pockets for phone, keys, ID badge, travel mouse, dental care items; 2 medium exterior pockets for wallet, camera, flashlight, pepper spray; 1 medium-er pocket fits a bi25 or other 1280 page paperback; big pocket can hold a few magazines; main compartment has plenty of room for half a Compact Oxford English Dictionary (...not that you would, but you could) or Rbi8, and the zippered slash keeps the important stuff separate from the mundane.

if you NEED a bigger bag then you probably should consider simplifying your life or getting a real purse.

that being said go with the charcoal, definitely the subdued elegance of charcoal...

updates
Oct-2013: students should consider the slightly larger version of this bag, mine is holding up nicely through mid-terms.
Jun-2014: no signs of wearing out, more like breaking in: the 'character lines' on the charcoal canvas are a nice effect.
Aug-2015: the zippy part of the internal zipper came off and the compartment now just comparts. haven't noticed a loss of function.