I've always had a soft spot for the metaphor of colors, rather then just shades; the idea being, of course, that black and white viewpoints represent all-or-nothing good or evil, shades show that characters have some-good and some-bad, while colors are required to question the whole legitimacy of "good" and "bad" in the first place. Not everyone uses the same scale, and all; there are many dimensions by which to judge any action.
Indeed... but I would say that for a character to qualify as a real anti-hero, the author must present him or her as not measuring up in some way. I guess this does involve passing judgement.
Otherwise– in the worst case– the character can become a full-fledged Mary Sue, perhaps acting out the writer's fantasies of not being bound by laws/ethics/social conventions/whatever.