No. Again, the concept of black Hardening didnt exist pre-TS.
Luffy just couldn't discern it.
Both black shaded and non-shaded CoA exist post-TS.
When Luffy didn't understand Haki in chapter 504, he couldn't discern Haki and Rayleigh's hands aren't black.
Post-skip, they are because Haki can be discerned.
It's not a literal colour, it's a visual aid.
As the manga said which you'd hvae to be in denial of, Haki is invisible as stated by Rayleigh.
And as stated by Hyo.