Colorblind casting is the right approach to theatre, I firmly agree with this. The world might not be ready for Raisin in the Sun to be translated to Vietnamese and performed entirely by Vietnamese people, I say go for it.

This works so well because theatre is a practice. Any play, even if it's performed once by one company (surely the mode for plays) is of the ages. Merry is black in your stage adaptation of the Fellowship, you say? Of course he is, everyone knew Isaac was going to get that role, he's a natural for it.

Cinema is a product, not a practice or a process. Like it or not, it makes a single, definitive statement about a story. It's fair to dislike it when those choices differ dramatically from those made by the author, including in matters of appearance.

If you think rabid fans won't be put off by 'trivial' things like an eye color mismatch, think again. You singling out skin color is your special pleading, reflecting your interests. I reject it. It is one of many aspects of casting in film which differs from the stage, for good reason.