@xan:
I never said it is a mistake. We don't exactly know which one is what i.e. with or without haki. All we know is that we were never explicitly shown the black coloring before the timeskip. Post timeskip, we get to see CoA being shown in black. We don't exactly know whether it is normal armament or advanced armament because we haven't been told explicitly that there exists such categories. All we know up till now is haki (black coloring) and without haki (no black coloring) that's it.
Before the time skip, we barely even saw Haki.
Post time skip, there have been enough appearances to safely conclude the Hardening part makes a difference. Otherwise, characters could just be shouting "Haki" or "Full Body Haki" instead of "Haki Hardening" and "Full Body Hardening".
Seems like a good way for a writer to needlessly complicate things for himself if both things are one and the same, doesn't it?
–- Update From New Post Merge ---
@HTC:
Not necessarily. Remember: Jimbe's attacks revolve around water in the opponent's bodies. It didn't work VS Akainu but it should work just fine VS Caribou specially since swamp has water, making him even more susceptible, no?
Tashigi also cut Monet without her sword turning black. Boo's axe was supposed to be coated in Armament when he broke it on Funk's back and yet it wasn't colored with black tint. Luffy knocked out a Pacifista without his fist turning black.
There are probably more examples around.