That's a nice one. As for rarity, of the 70s-80s colors, the browns tend to pop up the most. Hogsy and I are brownie fans among others here but I know they are not a huge among civilians and even some in here..
which could be why they pop up on CL more often then say an avocado or a yellow kettle.
Are you going to pick this one up? Looks like anywhere from 77-79 from the picture..
Oh and brown kettles aka Copper Mist came on the scene around 1969 when it replaced Chestnut Copperton (two tone pink) and were renamed Chocolate by the early 80s and still around as late as 1991 (N) code. I think they were still around a few years after that but it's unconfirmed.