I remember there were NPCs attacking Sierra and Cathedral some time ago on Requiem, maybe this has changed, I don’t know.
I don’t need to imagine anything, I met a player in wastes bazillion of times, trust me if you can think on your own, you don’t need any colors to alarm you. You see the nick, you see his hp/weapon/armor and if this guy is well equipped that means you have mostly two options: run or fight. If you get killed by someone, just tag him red thus he will become your mortal enemy and you can start hunting him down, but that doesn’t mean you should copy-paste his nick here, maybe he is a friend to half of this community, you never know.