People know it’s pretty common especially now a days for latinas and even Latinos to dye their hair right. The city I live in theirs a lot of blonde Latinas and Latino men. Highlights are pretty common to but I wouldn’t be for it given the explanation with Momoa was the sea bleaching his hair and I feel like it would take away from that.
That would be something if you auditioned for a role of a comic book character and complained of racism when the producers or directors reminded you what the comic book character looked like. I feel like if an actor made a stink like that, I'd hope that actor would be replaced pretty quickly. I think for a role where the source material wasn't so visually based, that might be more reasonable, but not for movies based on things like comic books, cartoons, video games, etc.
But back to seriousness, I don't think it's that uncommon to ask actors to dye their hair, or at least wear a wig. Cavill wore a wig for The Witcher, and I wouldn't be terribly surprised if he dyed his hair a shade darker for Superman. ScarJo's natural hair color isn't red, Jessica Alba isn't blond. I feel like unless during the casting process you're told you don't have to approximate the look of a famous comic book character, you should take into consideration that you may be asked to make some cosmetic changes.
Imagine if Zoe Saldana refused to go through the daily body painting before shooting after agreeing to play Gamora, or any of various guys said they wouldn't commit to working out and taking "vitamins"!
Cavill is white, and Zoe is playing a green alien, and working out has nothing to even remotely touch on PC issues (except "vitamins" - if you mean steroids then no way that flies at all in this day and age). It's different. And I'm not saying it is racist - just that in our hyper politicized world, asking someone not white to change their hair color to something only natural for white people (mostly) might feel that way to some people, enough so I think that they wouldn't ask.
And while it isn't uncommon, it also isn't common either. Barry Allen isn't sporting his comic book hair color on the tv screen or big screen. Bruce Wayne wasn't dark haired when Adam West or Christian Bale played him. Mamoa only had highlights for his Arthur Curry.
I'm not saying it can't happen or won't happen - I'm saying we shouldn't go in strongly expecting it to happen or be disappointed if it doesn't. It isn't the end all be all for Supergirl here.
IS she playing Kara or another version of Supergirl, like Cir-El?
In Zoe's case, the red hair and green body paint cover up her Black features.
IMO, if you audition for a comic book character and have a hard stance against changing your appearance to match the very popular visage of the character, maybe you ought to consider a different role. It's different if the director and producers tell you upfront which specifics aren't required, but if not, then I feel like the you didn't really do your due diligence/research before auditioning.
Yeah, Zoe Saldana auditioned for the role of Nyota Uhura. There's pretty obvious reasons for them to look for someone with a strong similarity to Nichelle Nichols. https://memory-alpha.fandom.com/wiki/Nyota_Uhura
The main difference in makeup is the hair styles chosen. Mrs. Nichols had her hair UP most of the time and Saldana has it in a long ponytail... that's the main aesthetic difference. But again... the people casting the film likely chose her for the role BECAUSE of her similarity to Nichelle Nichols.
Which leads to a different question: why did this actress get this role?
So? If it was a white actress it'd cover up her whiteness too. All part of playing a green alien from outer space - whereas the caveat here, the difference, is Supergirl is an alien that looks human.
Look, I'm not going to convince you that it might be possible that she won't dye her hair or wear a wig. Maybe she will. But if she doesn't, is that really such a big deal?
Again, TV/Film Barry Allen isn't blonde.