Personal preference, I suppose. My rational is that partial heterochromia is common in humans, so why not? If it is an issue, I'll remove it.
Not a big difference to me. Born it is.
I suppose that is true, but it's more about superiority than anything. When he was a Geshrin he was teased by the Yamataians. Now that he IS Yamataian, even though he is now on par with his past aggressors, he still has an innate complex with those superior to him, i.e. Nekovalkyrja.
Odd, yes, but he has a fear of other people in general anyway, plus the fact that his long-term goal is to prove himself useful. What better way to do that than to show up his "superiors" while in their midst?