A degree of uniqueness is colloquial, but what about axes of uniqueness? A purple human might be unique as might a green one. A human with 21 toes would probably be unique. Surely a single ever green person otherwise normal would be as unique as before if along came a single ever purple human who also had alone in history 21 toes. These are notable differences from everyone else. In conversation, though, how incorrect would it be to call one more unique than the other?
Also, there is the idea of uniqueness within a given set. You might be the only computer programmer in your household. For that set of people in your household, that single trait could be unique. On Perlmonks, being a programmer is not unique. Your account here is unique, but the same username might be used on some other site you or by someone else. Yet nobody else in the world has all the same traits as you.
You're unique among all humanity, just like the rest of us. ;-)