Oh, and Tauriel's hair colour?
I like
tehta's hair dye theory, but for those convinced elves do not die dye I think the simplest answer is that she's one of the Avari and descended from the Second Clan, aka the proto-Noldor. Possibly one of her ancestors was a close relative of Mahtan. Possibly not. 'Rare' does not have to mean 'confined to one