Fan Casting Red is Heroic in Sort by Tropes

Red shows up a lot when it comes to the heroes of a story, usually the color of their clothing. As their main color motif, it could also be their hair color, gear, Battle Aura, or body parts for robots and non-human characters. This could be limited to the main protagonist, or be as wide as an entire Badass Army. Some Chromatic Arrangement trios have the leader wear red. The reason is that red is the color of fire and blood, hence the color of action. Thus it conveys that the heroes are people of action as well (regardless of exactly how the heroism is presented in the show).