Don't take it personally, because the lack of "Salaam reciprocity" probably has nothing to do with your race, clothing, or any other factor which you can control. Go to any on-line Muslim discussion board and you'll find plenty of other people wondering the exact same thing. I don't know why so many Muslims neglect to return the Greeting, but some reasons might be:
- Ignorance of the rewards for giving Salaams
- Distraction (They don't realize you are even there until they've already passed you on the street)
- The person is of the opposite sex and will not speak to "strange" women (this one can be quite baffling. It kills me that some bros will not acknowledge a Muslim woman's salaam and won't even return it with a nod, but they seem to interact with non-Muslim females just fine.)
- Cultural reasons - some ethnic groups just seem to be more likely to return the greeting.
So ... don't feel bad. Keep giving the Greeting and reaping the blessings. If the Greeting is returned, so much the better!