It is Charcoal colored. He was unique amongst the Sith. When I was making my first pureblood, I tried to find a really black colored skin, but it doesn't get that dark.
Wow, nice one, totally forgot about that, although isn't it actually just really dark red, almost brownish, IE: the final skin option for Sith, or maybe I just can't remember.
You can learn more about King Adas here.