Obviously this is only as good as people make it: http://starwars.wikia.com/wiki/0-0-0
So I think it can be viewed as dark chrome, dark silver, black, etc. In reading the comic I never thought of him as black personally, but as a really dark gunmetal.
You can see here in this picture that Vader had black armor, and Triple Zero doesn't match. His color is in between the black and the silver on Vader's chest armor.
Capture by Iggy, on Flickr
And here:
Attack_the_base_triple_zero by Iggy, on Flickr
I know the toy is all black. Perhaps that can be a grey area (Dark Silver/Shiny Black Plating)
