How do you get a black ninja in ninja warz?

Answer 1

You give the ninja that you want to be a black belt and give him/her karma many times and will get a black belt.

If you want the black clothing style for your ninjas, You need to have chosen the Shadow clan at the beginning of the game. If you didn't you're out of luck unless you're willing to start completely over (you can go to apps.facebook.com/ninja-warz/reset to remove all progress in the game and get to pick a clan again. NOT recomended if you purchased karma or enlightened your clan.) This only works for the Facebook version as far as I (the editor of this answer) know, although something similar likely exists in the app version