Their eyes has never been the focus of their characters.
Mihawk has red eyes but Toei changed it for whatever reason.
Mihawk lived alone in a castle, he can be a descendant of one of the 20 kings or even Imu.

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The moment Oda showed Mihawk getting super pissed off at the Reverie about the Shichibukai dismissal, everything became crystal clear to me who he wanted his final villain to be. The eerie music while the readers got swayed by Mihawk being a "nice" person to Perona telling her to take care of herself (to leave) gave me all the confirmation and affirmation I need. Really reminiscent of Aizen being "nice" to his subordinate at Soul Society before "that" happen.
The only question I had after that was "Are you really gonna do this Oda." and I laughed. Because I knew if I was Oda, I would have done exactly that. Days, weeks, months, years, and I manage to found HUNDREDS of connections between Mihawk and Imu, that the majority would never have been able to find and decipher.
Some people argued "No Luffy should be the one to fight Imu not Zoro!" to which I was reminded of Naruto, Sasuke and Sakura all fighting Kaguya and Madara at the same time, or when Goku and Vegeta fought the final villain together as well.
Luffy will become the Pirate King (df will be > Imu (mihawk)'s non sword powers like in 1085).
And Zoro will become the Greatest Swordsman (sword skills levels will be > Mihawk's).
after their victory against Mihawk (Imu).
Luffy and Zoro the only two strawhats who fought Mihawk and Lost.
History will repeat yet again, and the two will fight him once more (however many) and eventually Win.