how do I start a color gang?

I would not recommend starting any kind of gang. People can get hurt or even killed, and there's a lot of things you don't want to deal with.

yea its a bit iffy, you could start one up with no ill intent, but the problem is that other gangs may not have the same value, its not recommended as the squirrel said.

basically a gang is just comprised of multiple people with the same beliefs that stick together, and of course wear something of the same color to show their membership and support, larger the number of members, the higher the chance of being noticed.