I wouldn't worry about becoming vain. I think if you are concerned you that you may be vain then you're probably not. Generally, I think vanity is one of those slippery little beasties against which a healthy dose of self- awareness is good protection. Coordinate if you will. In fact, you are probably doing yourself a favor. People are extremely appearance conscious, and by paying attention to your looks you might just give yourself a leg up in those all important first impressions that can sometimes be the difference from someone thinking "hm, charming lass" and "oy. that person is sloppy and inconsiderate." Irrational as it may sometimes be, people (most especially of the NT variety) seem to think that the way another person dresses is a direct reflection on how much that person respects the other people with whom they come in contact. They may not consider that some styles of fabric or clothing are very uncomfortable for people with AS.
Ultimately, you have to go with what makes you feel good and what you think looks cool. If that's a blue streak in your hair, I say go for it.
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"Well, it's... meretricious."
"And a meretricious to you, kind sir, and a happy new year!"
Well played, Watson.