National armies would literally line up facing each other in uniforms with literal X-marks-the-spot targets.
The reason for armies meeting up like that, and in bright colors, is to avoid friendly fire, not because of honor or anything like that. When you have a bunch of peasants dragged from their homes and shove a musket in their hands, anything more complex than “Holy shit, holy fucking shit, do NOT shoot or stab the guys in BRIGHT RED, only those in BRIGHT BLUE” tends to get lost in the chaos of battle.
The reason for armies meeting up like that, and in bright colors, is to avoid friendly fire, not because of honor or anything like that. When you have a bunch of peasants dragged from their homes and shove a musket in their hands, anything more complex than “Holy shit, holy fucking shit, do NOT shoot or stab the guys in BRIGHT RED, only those in BRIGHT BLUE” tends to get lost in the chaos of battle.