Aramaki may have a black sword and this can be used as proof. Yet, I'd like to point out three things.
1. Why would Aramaki need a black sword if he has a Devil Fruit and vice versa?
2. Aramaki does not aspire to me as the guy who would turn a blade black. Even Shanks, who is Mihawk's closest rival, did not turn his blade black. Heck, even Roger did not have a black blade. Turning your blade black is the pinnacle of swordsmanship, this was only achieved by the God of the blade Ryuma and by the World's Strongest Swordsman Mihawk. I don't see Aramaki, the guy whose sword was not even named or called a black blade have one.
3. Let's not forget that the "official coloring" can also be wrong.