The earlier experimental versions of this round had several tip color variations. The XM276 tip colors I am aware of are pink, white over pink, green over pink, and green over white. The green over white was a marking error from what I recall - it was supposed to be green over pink. The ones I have seen with these tip colors have been from FA and LC with late 60s headstamps. Sorry I can’t be more specific on that - I don’t have my references handy right now.
I have also seen a green over white tipped round with an LC 92 headstamp that was listed as a dim tracer. I think I will ask about that in a new thread, since I’ve been wondering why the color coding error would be repeated 20 years later.
I’m not sure if it was ever an official designation, but I’ve heard people refer to these rounds as starlight tracers as well as dim tracers.
I hope this helps!