Nothing of that indicates there is black CoA; stop twisting the statements.
What exactly I’m twisting?
Your arguments are the following :
1/The black color of haki is a visual cue for the readers to indicate that CoA is used
2/The people in the One Piece world does not see CoA as black
3/We could not see the black color pre-TS because Luffy was not aware of CoA but we can see it now because Luffy is aware of it.
To defend this argument
@HPsyche used Rayleigh destroying Cemie’s collar. When we first saw this scene throughout the « oblivious about haki Luffy » eyes we saw that Rayleigh’s hand was white but when the «knowledgeable about haki Luffy » reminds him of this scene we saw the black shading.
My counter-arguments are the following:
1/There is no such statement by Oda
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.
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.
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.