Since I have no real need to say that a person is good or evil, and since the chaos/law dichotomy is entirely false, this is what I think about when adding an alignment to a person. Why? Because it works, in game and out. And that makes it a success. Sure, you can continue adding layers upon layers to it (see Ghostwheelz's suggestion for a good/bad side of each color), but at some point, you need it working. And IMO, it's a useful personality test after alignment is dealt with.