I like the American football analogy fearn.
Sometimes the act of preparing for war is a psychological boost.
War paint can cover a lot of different roles, but that may be one...
I know that when confronted with an imminent fight... it is sometimes a morale-raiser to compose yourself, look over your weapons, and prepare yourself physically. For some that is the split second between seeing the mugger and reacting... for some it is having the fists wrapped and gloves put on... others still it is checking the switch blade, putting on the mask, and saying a quick prayer... for others it is carefully checking ammo and gun, wiping down equipment, and applying the camo-paint to the face...
Perhaps putting on the war-paint is akin to carefully putting on your armor, or saying a prayer, or wiping down your gun... it might be a bad idea to make equivalents with different warriors of different situations... but as long as we understand it is it's own act and has it's own consequences that are not the same as the above, I think it's ok.
Perhaps a similar thought would be indigenous tattoos that have to do with masculinity and warfare.