If you read what Gyukimaru said, he said a Black Blade (literally coloured black) is forged through battle.
If you listen to what Hitetsu said:
The user is who determines whether a blade will raise in rank and become a black blade.
Difference between Wado Ichimonji and Yoru/Shusui is they were blades that became Black because of their masters and Wado Ichimonji is a blade whose rank has not been raised. It's just a well crafted high graded blade like any other high grade blade that's yet to be forged into a black blade.
Never said the Yoru wasn't actually black if you read what I said.
I said Haki is not black literally.
That's not the same thing as saying Shusui or Yoru aren't literally Black.
Nope, it's just shaded black to show the level of Armament being used.
Regular Armament is invisible, but not shaded.
Hardened Armament is invisible, but shaded.
Armament Haki is generally invisble.
When Zoro uses Armament or Hardening, his blades are still the same colour.
A blade becoming a Black blade? That's something else entirely. That's not Haki.