User blog comment:Kaido King of the Beasts/Chapter 864: You've Never Had an Enemy Like Me/@comment-26219137-20170503033634/@comment-173.218.64.42-20170503074644

It was armament haki. He was shown with the darkened skin in this chapter, but I remember him punching Caribou who is a logia user. So him having it isn't really a new revalation. Good eye though.