No he can even possess supreme grade meito like Fuji although he seems to be more reliant on his df a lot more i would buy it
Kokutos on the other hand is reserved for the very best those who reached the peak of swordsmanship i don't see him on that level
I will be more or less fine if it's revealed in the future as a white supreme like Fuji's
But, until proven otherwise, as it stands it is a black blade for me
Even though there may be strong arguments against his black blade ( like the bolded line of yours ), any argument is outweighed by the fact that Oda drew his blade as a black blade, with him not using it in the page before :
I remember Ha001 tried to counter Ryo's BB by saying it could be black cause he used it a moment before with hardening like Raisin :
But this argument doesn't work cause Ryo didn't use his sword in the panel above
So far Oda is also following Movie ( Gennai ) Aramaki's behavior of not revealing his sword skills until the end (
it's said nobody except Gennai Aramaki's GF ever saw his sword skills ), making it more likely Ryo didn't use his sword vs Beasts Pirates
If Oda wants to keep the
bolded true, he could've still made Ryo use his sword skills vs Beasts Pirates, as long as he kills all of them, but we know King is alive
If Oda's consistent with this behavior, then i guess we're only gonna see his sword skills during his final appearance - i guess when SHs defeat the Marine HQ
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It is black everywhere it's shown too - B & W Manga, Official Event Wall, VC, Official Colouring
So we can rule out that Oda coloured it black by mistake
In ch. 1054, in the little bit of the sword visible, it is also black like this :
How did he turn it black i don't know, it's not even confirmed he turned it black himself, maybe it was turned black by some WSS who lived sometime between Ryuma & Mihawk
Although for now i assume he turned it black himself