Oh, thank you for that! We're still working on catching links that still go to LJ -- I'll fix that one right now...

Okay, though, as for the question itself... Really, we mostly handwave these things. We have a character with blue hair whose hair is died (although that's canonly not her natural hair color) and a character with blue hair whose hair just... Is blue! In fact, I'd say a majority of characters with unusual eye or hair color have this be a natural part of their character. Hope that helps!