Start looking at 'neckerchiefs and gangs' and it's easy to drown in the flood of information that comes your way.
Gangs, and motorclubs, are probably the best known (and consistent) users of neckerchiefs these days. Gang colors are the types or color of clothing, neckerchiefs or insignia that are worn by gang members to identify each other. Tattoos may also come under the category of gang colors.
Street gangs wear many colors, for example the Sureños wear blue and grey, and their rivals the Norteños wear red and black. Bloods wear red. Their rivals the Crips wear blue, the Bloods' allies the Latin Kings wear gold and black. Latin King rivals Folks Nation also wears blue and black, and are allied with the Crips. Other gangs such as La Primera wear white as their main color. Their rivals the Cholos wear all black. Etc, etc.
Here in NZ the various (Maori) gangs like Mongrel Mob (Red) and Black Power (Blue) have their own colours and symbols, often linked to Maori traditional symbols.
Motorcycle clubs wear their colors in "cuts". Denim or leather jackets without sleeves emblazoned with patches. Generally the club logo is centered on the back with banners known as rockers reading the name on the top and location on the bottom. Often an "MC" for Motorcycle Club sits next to the club logo.
The front of the club cut can feature a myriad of different patches with different meanings based on the club. Common ones are 1%er patches for Outlaw clubs as well as patches denoting rank or deeds done.