A) VERY delicate sketches of non-objectionable personality traits (like a hint of wryness or world-weariness)
B) NPCs that behave as if your character has a distinct personality while not doing so in ways that actually identify what it is
C) one-sided relationship-building
Needless to say, a lot of the color comes from NPCs' relationships with EACH OTHER, even though we try to keep it centered on the PC as much as possible.