@Bruce:
I might get bashed for this, but seems like this is the best place to ask.
Why use "Color of ______" when referring to different Haki in English? To me, it's similar to saying "Lakers type of jersey". Sounds kind of redundant when you can simply say "Lakers jersey".
So why not simply use "Armaments Haki", "Observation Haki" and "Conqueror's Haki"?
Just people's personal preferences, is all. One of the translations called them "Color of …" and people like to use the "official" name, so they use what seems to be the closest they can get in English.