The colors that RJ teased are Slate and Evergreen. As for which vehicle it shows up on, my guess is R2. R1 already has two greens and two grays. Just my 2₵
I have LED trailer lights and it works just fine. I’ve found my 7 pin adapter is a PIA to seat properly in my R1S. I assume you’ve inserted it VERY firmly into your Rivian’s connector? My Jeep GC wasn’t this this difficult.