Is it true that US tracer rounds were red and VC green during Vietnam war?

Read this article from Vietnam Magazine: https://www.historynet.com/tet-1969-at-cu-chi.htm I was also there. When the alert sounded, green tracers were going over my head when I dove into the bunker. Later, as Spooky was flying overhead, green tracers rose to try and hit the plane. Spooky replied and the VC firing stopped. Spooky was using red tracers. It sounded like a chain saw spitting fire. I have slides of this happening.

I can't verify that all NVA/VC tracers were green, but I certainly saw them using green tracers to hit the ARVN compound below us at Dak To one night around May or June 1969. The outgoing ARVN tracers were the usual red, while the incoming commie rounds definitely appeared to be green. It was fascinating being able to relax and enjoy the show. We had other things to do when the incoming rounds were coming our own way.

Here's a thread on ar15.com (a gun enthusiast forum) discussing it, and coming up with a variety of experiences both confirming and denying the NATO: red, WarPac: green mantra.
Here's a vendor selling both NATO and WarPac ammo, with both red and green tracers on both styles.
There are also other colours in use, though seemingly less common, such as white and orange, with infrared tracers becoming more common as night vision equipment becomes ever more widespread.

To make matters more confusing, the round will have a different painted tip or ring around it to identify it as a tracer, which may or may not have the same colour as the trace itself (so a red-tipped round may burn green and v.v.).

A tracer projectile is constructed with a hollow base filled with a pyrotechnic flare material, often made of phosphorus or magnesium or other bright burning chemicals. In NATO standard ammunition (including U.S.), this is usually a mixture of strontium compounds (nitrate, peroxide, etc.) and a metal fuel such as magnesium. This yields a bright red light. Russian and Chinese tracer ammunition generates green light using barium salts. Some modern designs use compositions that produce little to no visible light and radiate mainly in infrared, being visible only on night vision equipment. However, one cannot see the tracer that is heading for or near you. In modern times the majority of tracer ammunition is red/orange, with the exceptions of decades old ammunition. Note; during the Viet Nam conflict the "VC" did not manufacture their ammunition. It was purchased/issued via the USSR and or China, hence the green tracer.

During my time as a grunt in the 25th infantry in VN, I saw several night engagements. The Cong/NVA tracers appeared to be green, and the GI tracers appeared to be red. However, when engaging in firefights during daylight, the GI tracers were orange in appearance. I suppose that has a lot to do with the amount of ambient light. During the day, I never witnessed Cong/NVA tracers.

The night fighting was something to behold. The strangest one I witnessed occurred while my unit was in the field, dug in for the night at the edge of a banana plantation, overlooking a large valley. It was about 2100 hrs, during the Winter, so very dark. We heard a blast a long way off, and one of our other units, about a mile across the valley, engaged a Cong/NVA unit, from a distance. They were probably about to 200m apart, and were throwing all they had at each other's position. It was one wild light show, and lasted maybe 3 minutes, which is a long engagement. I found out later it came about when our friendly's Claymore booby trap set up about 200m down a trail from our friendly's position was detonated. They opened up on the location of the blast, and the enemy returned fire to the origin of the red tracers. So, each was slinging a lot of lead across a large space. Once arty was called in on the claymore position, the fight broke off.