I know at least in my school (being the most diverse school in the state), there are no such lines drawn with skin color or race.
If I am walking at night and I see a group of black kids, I'll approach them with the same caution I approach white kids. Caution.
That does not mean you should run in fear, but if you truly feel you're in a dangerous situation then get yourself out of there. It's common sense.
I don't pin teenage violence on any specific race, since in my school I have seen it spread evenly amongst everyone. I attribute it more to the lack of a home environment and parental neglect.
If you're raised on the streets, all you will know is the streets. This is something that I've seen proven correct time and time again by the people I communicate with on the daily.