User blog comment:XV DEaD ShOT xV/Why Lucy Appears Blue?/@comment-3981209-20121104192743

I thought it was due to hostility. This debate's been going on a while, looking as far back as Al Mualim appearing blue, and therefore I think that it is related to whether the person intends to harm the player. For example, in Haytham's Eagle Vision, Charles Lee and the others are blue, but they're red in Connor's Eagle Vision.