I've went under a great variety of usernames for various reasons. Kuro is one of the third longest-standing usernames I've had, though. 

Was watching Railgun at the time and a spur-of-the-moment decision happened and I borrowed the Kuro part of Kuroko's name. Now it happens to be the name I use practically everywhere, with variations here and there should the name ever be already taken (as most short names are).