WOW! I think the others here have answered this question with excellent responses. I was going to say much of the same things. I think this great that we keep posting information about gangs, because it is ignorance of the subject that will get people killed more often than what we typically think of as a "real-life self defense scenario."
It really is not so much about looking for gang colors, but being aware that wearing the wrong colors in the wrong neighborhood can get you killed. Gang members pretty much know who lives in their turf, and who is in their gang (with the exception of larger cities where sub-factions of the same gang are more spread out). They flash unique gang signs with their hands, and use other subtle methods of identifying each other, but I think it is done more to warn of other gangs trespassing in their neighborhood. The way a bandana is worn, the pocket it hangs from, or the direction that the bill of cap is pointing on their head is just as much an indicator as the "colors."
At clubs and other places where rival gangs might meet up, clothing and hand signals are more to tick off the other gangs, establish territory, and even to provoke fights. Innocent people are often targeted just because they don't know they are in gang territory, or that they are wearing a color of a rival gang (be neutral in colors, or find out from police what colors and symbols are used in your area, or where you might be traveling).
The fashion statement mentioned by jks is one of the problems that gets people in trouble. Often times, non-gang affiliated kids will think they are being cool by dressing with the "gangsta" look, or like a favorite rap artist only to unwittingly show some kind of dress pattern, color, or tip of a hat that represents a rival gang - - and they are knifed by a passing gang member, or shot in a drive-by. One of the problems within the gang culture is that they are constantly recruiting new members, and this might require them to commit a crime such as assault, armed robbery, rape, or even murder just to get into the gang. Anyone can become a target. We've had several such problems in our area in the past. Also, drive-by shootings pop up out of nowhere, and innocent bystanders are often the victims.
It has been said that many of these colors, symbols, and gestures are different from place to place, but also can change from year to year, or month to month. The best bet is to learn where heavy gang activity exists, and avoid those areas (especially at night), and contact any local police, or gang task force that collects and distributes current information about gangs in your area.
CM D.J. Eisenhart