I defiantely agree with the mood thing. I'm more likely to wear black if I'm in an antisocial or depressed mood, and bright colours when I'm happy. But I do buy clothes that I think reflect who I am, whatever that means.
Maybe you could say someone who always wears a suit all the time, even on their days off is someone more highly strung or proud, and someone who wears joggers constantly as laid back. Hm.