User blog comment:Master Sima Yi/Assassinews 19-03-'14 – Two Assassin's Creeds for 2014?: Unity and Comet/@comment-138.210.203.162-20140327004627/@comment-5174994-20140330001259

Blue was also a common colour of the time, so that helps for blending into crowds. Being able to blend better in the night also makes it more realistic when the enemies can't see you in stalking zones.