I’ve heard that the overhead fire tracer with a red tip lacks a base closure disk, which could come off and endanger the troops who are being fired over.
As far as the starlight/NV/IR/Dim tracers, I don’t know if there are official differences between them. I always thought that they were the same thing. I have the following rounds in my collection:
pink tip, + FA 68 (XM276, 1st type)
white over pink tip, + FA 68 (XM276, 2nd type)
green over pink tip, + LC 69 (XM276, 3rd type)
green over white tip, + LC 70 (XM276, 3rd type, color coding error)
lilac tip, + LC 97 (M276)
Scranton’s “Small Arms Ammunition Identification Codes” says that the type 1 XM276 traces to 550 yards, the type 2 traces to 1100 yards, and the type 3 traces to 930 yards.
I have the green tracer as well but no information about it, other than the green trace was intended to confuse the enemy during Desert Storm. Mine has a brown tip and a + LC 91 headstamp.
There are several other experimental 7.62x51 tracers listed in Scranton’s book, including a long range (FALRE - Frankford Arsenal Long Range Experimental) with a white over red tip.
Some day I want to enter the basic info (caliber, type, country, color code, page number) from Scranton’s book into a database so that I can pull up an index of all US tracers, for example. There are lots of neat cartridges in there that I will probably never see in real life!