The gold is conqueror's haki and the black lightning coming out of Kaido's weapon is CoC coating, Luffy has the aura and the coating, not that hard to understand.
As for why Kaido doesn't have the aura, maybe it's a Luffy and Zoro thing, if Yamato gets the aura then it's a good guys thing.
That's when the nΒ°4 got CoC, ryuo and FS, all at the same time. They forgot to give him the platinum aura.