Colors
It used to be that the color of small arms tracers told the country of origin of the ammunition. Purple came from Eastern Europe, and was to be avoided at all costs. One of the problems with using captured weapons was not only the sound would identify one as a bad guy, but the tracers would, too.
So, I was thinking that tracer color could be used to ID the folks shooting. I doubt if in Afghanistan the allies would be using bad guy ammunition, but then, again, friendly Afghanis might. Oh, well, it was a thought.
Arf