Rogue

From BZFlagWiki

In BZFlag, rogue is a team players can join (if allowed), though they have no teammates, and can kill any and all tanks, including other rogues. The bullet color is yellow, as is the tank on the radar. The tanks themselves are a dark gray/black color, in the usual tank pattern.

On most CTF servers, the rogue team does not have a team flag, but there is a plugin that adds a Rogue Team Flag.