Re the white t-shirt thing...it's been the standard summer fare in my 'hood for the past 5 years too. I always figured it was because when you get arrested the local jail will only let you keep a plain white t-shirt and those jump suits are itchy I've been told.
The friends I have (and me) do own white t-shirts.
But thats only because they're cheap, easy to clean and easy to replace.
If its a designer shirt or something, its not going to be something you want to get dirty.
I've worn solid black and solid white t-shirts since I was a kid, along with all the designer labels, it was never a fashion statement, just cheap, easy to replace, easy to clean and something you don't worry about.
I doubt any thug would have the brains to think they could start a fashion fad or follow one just to make get aways easier.
Sidenote: There was one thing some local thugs started doing years ago, they would wear different clothes under (tear away) jump suits, so they could run, pull off the tear aways and look totally different, but that died a quick death (ain't easy running with 2 layers of clothes).