Are you belting it/does it come with cinch straps on the side? Might make sense to have matching colors there...

I encountered a fellow and his wife in a similar tartan, Buchanan. They had matching leathers in the medium brown of the boots you show. Either way, I would go with a very light tan or nude color on the tights-less exclaimation, more transition-black or white would likely take away from the tartan and boots both.