Nah I’m holding firm, that is clearly an anime error. The anime has made coloring mistakes before as they did with Kuma’s color scheme, Marco’s initial design, drawing Saint Shanks with two arms in the Whitebeard flashback, Fujitora’s color scheme, etc.
Call it cope, I don’t care. If Oda shows or says that it’s not a black blade then that’s one thing, but the anime has made mistakes before and this is one of them. It is clearly a black blade in the canon manga.