Well, in B&W manga Ryo's blade is drawn EXACTLY like a black blade, there are actual comparison pics. His incoming figurine depict it as one too.
And studios that make legit figurines (not bootlegs) always have contact about Shueisha to get the official color schemes.
If it's not a black blade, Oda drew a sword that looks exactly the same as a black blade... because troll I guess.
Why isn't he using it? I don't fucking know, he was never pushed hard enough to maybe.