Answer:
I mirror your actions.
I've been argued on my color. Without me you'll die. So many attempts on your life use me so make sure you have many of my White friends.
I am a king who's good at measuring stuff.
I can swim but never get wet. I can run but never get tired. I follow you everywhere but never say a word.
I am your most powerful weapon; I come before your eyes. I help you seek the truth, yet I often give you lies. What am I?
When is it bad luck to see a black cat?