This might be the worst cope I have ever seen.
You don't use the manga, which is black & white, to confirm the color of something. I can't actually believe this needs to be said.
It could very well be a black blade but the only time you'll get the actual official color is when Oda colors it himself.
Even the official colored volumes(made by colorists) have been wrong at times. Big Examples being Gaban & Jupiter having blonde hair in colored volumes while in actuality, Oda later on confirmed their hair to be gray.
Even recently, people were saying Loki's weapon was black & potentially a "black hammer" only for Oda to confirm it to be grey.
So, if you want the actual official coloring, 100% verified, then only Oda can do that.