There was a rumour a while back about a matte dark green variant for the Pro models but I think it may just have been one publication mixing up the Pro and XR replacement colours.
I think the Pro models, since they look to have largely the same design as the XS, look best in silver - though it does seem to the be least popular colour option. The plain stainless steel band gives it a completely timeless look IMO and it’s the only one of the current lineup that I think looks better with age and a bit of wear. I haven’t liked any of the gold options and, again I realise i’m in a minority, I think the XS was the gaudiest gold yet.
I love all of the XR colours on the glass backs (though i’m less keen on the colour matched aluminium). The latest mock-up of the green option - much darker than previously rumoured - looks awesome.
All that said, i’ll be sticking an Apple leather case on so it doesn’t actually matter too much.