Generally ethnicity or color doesn't matter, except in terms of how much a character is a favorite for me. For Wonder Woman, Gina Torres is a fine actor, but doesn't look close enough in terms of color only because I want any actress to look as much like Wonder Woman of the comics which Lynda Carter did.
Well, Wonder Woman has looked a lot of different ways in the comics. Carter bore a reasonable resemblance to how Diana looked in the '40s or the '60s, but the modern rendering of Wonder Woman is far more statuesque and, well, Amazonian. Carter's look and build just wouldn't fit the modern version of the character. Not to mention the personality -- Carter's gentle, girlish persona worked for a Wonder Woman of the '70s, but a modern Diana needs to project great power and authority and the toughness of a warrior as well as deep warmth and compassion.
I mean, really, it should be axiomatic that an actor's apperance isn't as important as their talent and personality, their ability to convey what the character needs to be. If it's a choice between someone who looks just like the character but can't act, or is totally wrong for their personality, or someone who looks significantly different but just nails the essence of who the character is as a person, then you pick the latter. I didn't just like Torres as Wonder Woman because of her height and physique, but because of her great talent and charisma as an actress and her ability to capture everything that defines Diana's personality. I've seen her portray deep warmth and kindness as Jasmine on
Angel and great power and warrior presence as Zoe on
Firefly and other roles. She fits well enough in personality that the fact that she only loosely resembles the character physically is of secondary importance. Fixating exclusively on appearance is fine if you're casting a model for a photo shoot, or a booth babe for a convention. If you're casting an
actor to deliver lines and convey a character and make an audience care, then it should be obvious that there are more important considerations than what the actor looks like.