Forest Green and Limestone were also my finalists. I went with Limestone/FE at the end because it seems to be the “younger” color ?. And I always dig the cement color on a vehicle. But yes it’s another greyscale color. You can’t go wrong with either.
seen both up close multiple times and a friend of mine has the Limestone. FG is more of a "common" color. it is a shade of green unique to Rivian but you'll see other manufacturers with a dark green thats similar. Limestone is similar to other flat blue-grey, green-grey vehicles that seem to be popular over the last few years but probably more of a rare color.
Limestone was my choice until i saw it in person and it was too light for me and didn't feel like it would age well. for example, Toyota's Lunar Rock, was really cool to me when it first came out but now i think it looks dated/drab. and other greys kinda all look similar.
i will say both Limestone and FG both look better with matte PPF but imo, matte on the Limestone makes it look even more plain grey while FG looks stunning so if you plan to wrap it thats another thing to consider.
keep in mind the Limestone in most pics taken by phones doesnt look like that in person so definitely try to see it for real before making a decision.