Cédric Ido comes from Stains, near Paris, once considered one of the worst cities in France, with a lot of gang violence, in which he lost a few friends. He wanted to show that these neighborhoods are filled with people with real talent (Joshua is an engineer, Daniel an athlete, Christophe an artist), but because of social determinism, their talent couldn't be seen nor exploited, and will eventually go mostly unused.
The color red is quite present in the movie: in the sky and on the Ronin gang's hair. Director Cédric Ido was very influenced by Japanese movies, be it from Akira Kurosawa, Kenji Misumi or Kaneto Shindô, and in Japanese culture, red is used to ward off demons, but also a symbol of defense and healing.