1/The black color of haki is a visual cue for the readers to indicate that CoA is used
It's only for Hardening it's used as a visual cue.
Many instances where non-shaded Haki is used post-skip.
Bobby Funk explicitly states he used Armament haki, yet his sword isn't Black.
Luffy against Caesar, invisible haki.
Tashigi cut Monet in Fishman Island without Black Armament.
Burgess attempts to stab Sabo who he knows is a Logia, there's no way it wasn't imbued with Haki if he hoped to be successful.
Post skip, it's not shaded when it's the weaker version and it's shaded when it's the stronger version being used.
2/The people in the One Piece world does see CoA as black
Franky was present when Lffy used Hardening (Shaded Armament) to punch Surume the Kraken.
2 arcs later, he's surprised Luffy can use Haki.
Clearly, if he saw Luffy's hands were Black on the way to Fishman Island, he'd know that Luffy was a Haki user and not be surprised in Punk Hazard.
So, nope, people cannot see Haki.
It's sensed. It's not literally black, thus why it's said to be: Invisible.
1/There is no such statement by Oda
That's a fact.
Name one crew with Haki users, and show me where the strongest wasn't capable of using Shaded Armament. You'll have your work cut out for you.
2/Oda created a character named « Zephyr » this character epithet was « black arm Zephyr » because he was a proefficient koka user. Which means that in-universe people were seeing Zephyr’s arms turn black this his epithet.
Same movie, we saw Luffy destroy Kaiorseki.
Even Shiki, 1 of the 3 greats in the last generation had to cut off his legs to escape out of Kairoseki.
Films are films, they're not canon information.
3/Yes when the « knowledgeable about haki Luffy » remind himself about the Camie scene we saw that Rayleigh’s hand is black but it actually prove that the black color is actually a thing because when the « knowledgeable about haki Luffy » remind himself about his fight with Sentomaru or Rayleigh vs Elephant, the black color is not there :
If in one souvenir the hand turn black and in another souvenir the hand stayed white that means that the black color exist in-universe.
If in one souvenir the hand turn black and in another souvenir the hand stayed white that means that the black color exist in-universe.
It doesn't prove it's a thing, it just indicates the level of Armament being used.
Like Rayleigh and Hyo said, it's Invisible which most of you are ignoring because it doesn't align with preconceptions.
Now if you want to entertain the idea that blades are turn permanently black due to the number of fight they have been, be my guest. But that would just means that Mihawk has more fight in his life than :
-All the Sandai Kitestu users combine
-WB
-Roger
-Shanks
-Oden
-Big Mom
-Fujitora
And had as much fight than a guy who was singlehandely protecting an entire island from the world even tho he has been a Shishibukai for a certain numbers of years.
-All the Sandai Kitestu users combine
-WB
-Roger
-Shanks
-Oden
-Big Mom
-Fujitora
And had as much fight than a guy who was singlehandely protecting an entire island from the world even tho he has been a Shishibukai for a certain numbers of years.
If you read the entirety of what I said, I said the one fact we're told is a lot of battles is one of the prerequisites for the forgery of a Black blade.
We have 1 thing that is definitely a prerequisite and we have various hints. Battles is just 1 fact we know is necessary, but what else besides that? We don't know factually, we just have hints.