Tracers have a red tip, AP have a black tip. Not sure about API (armor piercing incendiary). The ratio of round types depends upon the armorers/ordnance handlers. Those are the guys who link up the ammo. I have read of some pilots who did not like to use tracers at all in order to not spook their target in case they missed with the first burst. Others may want a particular ratio of say 3 Ball, 1 Tracer, 1 AP or API.