Mihawk was talking zoro not drinking until he learns haki
The black blades thing wasnt related to hardening
No proof color is visible
The black blades thing wasnt related to hardening
No proof color is visible
I mean, the entire context is about Zoro coating his swords in haki and Mihawk saying Zoro can't drink until he's mastered "the feat of turning every weapon into a black blade".
So either;
- Zoro broke the rules and drank anyways
- Zoro made a secret black blade
- Or haki is visible