It seems that people are very good at visually keeping track of a group of objects -if they are of the same colour. So members of a rugby team can gain an instant sense of whether they have an ‘extra man’ locally on the pitch…just enough to stretch a defence thin enough to get past.
This may have had some interesting effects, too, when each army fought in its own, uniform colour. You could see if you were faced by more people than were in your platoon and decide to retreat, thus avoiding unnecessary defeat. Now everyone’s military are clad in a common camouflage, so that being able to track one’s comrades, or opponents, is outweighed by keeping everyone hidden from the enemy.
Today’s invention is a drone aircraft carrying nontoxic paint which it sprays on anything which is deemed suspicious in a given area. It thus avoids accusations of harming noncombatants, whilst highlighting people (and weapons) in a longlasting, dayglo shade. Spraying soldiers in a shocking pink might provide an additional benefit via its demoralisation effect on the notoriously fashion-sensitive military.