In the world of sweats, grey is the standard. The color not only shows better heathering in the fleece, but it also speaks to how informal sweats are. (Just check how awesome grey Nike Tech Fleece pants look.) But these aren't the ones that should be worn to the office. As much as it pains you to buy black or navy or charcoal sweats over heather grey ones, it's the better move for wearing them to work. At first glance, non-grey sweats might even pass for real pants, and that's the goal.