Its not great when he himself fogets to draw shit himself, "ohh now in this scene you cant see haki but in the next you can" yeh get away with that shit Oda just stay consistent.
It is consistent. Just pay attention to the manga itself and not fanfic writers on forums and youtube.
You see Hardening because it's a specific move that makes haki visible while physically hardening the body part/item its used on. Dressrosa clarifies this with Mihawk's "every blade can be made black with haki" dialogue as well as the debut of Gear 4 when Luffy using full-body Hardening
physically changes the properties of his rubber which lets him do different compression-based techniques that he cannot use without Hardening.
People with the ability to use logic can read these 4 consecutive pages from Punk Hazard and realize that when Luffy draws blood from full-Logia Caesar and Caesar says "that hurt!" he's using Haki, and that invisible haki is a different technique compared to Hardening. You can even see Caesar
look at the black coating with his eyes and panic.
People with water in place of a brain read these 4 consecutive pages and go "uhhhhhh i guess Oda forgot, because the black coating is just for the readers" (some shit Oda literally never said, entirely fan headcanon, complete bullshit that spreads from youtubers, doesn't even make sense because when people like you try to make this work logically it doesn't work, because they're different fucking techniques lol)
