I think the problem is that once you alter the skin colour, no matter how many of the other characteristics of the character remain, there's going to be a disconnect that's hard to overcome. For instance, I follow a lot of cosplayers on Instagram, one of them, a Caucasian girl, did a Storm from X-Men cosplay. Everything about the costume looked like the Storm from the comics, the outfit, the cape, the hair, all of it. But by virtue of her skin colour it didn't register as Storm in my mind, it's someone dressing up as Storm yes, but it never felt like the character. And this goes across other types of characters. A blonde girl in a Supergirl cosplay looks like the character, whilst a brunette looks like someone dressing up as the character. There's nothing wrong with people dressing up as characters who don't look like them, but IMO there's a break in immersion compared to someone who does look like a character. One comes across as authentic, the other is someone playing a part.