IF you are going for an authentical theme in your movie/show that is an okay standard to have. If, for instance, Rome had cast a black Caesar (A person, with actual ancient sources on what he looked like), that would have been really weird, since they payed alot of attention to historical colors on houses, the type of food they ate and so on.Nah, it has to do with historical accuracy. Some of us find it odd when they go out of their way to cast, say Heimdal as black, (Elba is a great actor though). Why do they have to base the story on a country's myth and then cast etnical groups that don't belong there. Granted there were for sure africans in ancient greece at the time, and Spartacus balances this well, but having the, (mythological), founder of the city Rome as a black is beyond me.
Marvel comics and most TV shows do not pay any attention to historical accuracy in any regard (I teach ancient literature, it hurts sometimes! ). Thats okay. That means they can have as many horns on their helmets, black actors, Emperors from completely diffrent periods, the fucking sword of TROY and whatever else they want to put in there. Complaining about that makes about as much sense as complaining that there is only 3 people in Caesars army in your local school play.
I dont know what this show is going for, but IF they care about "history" at all in other regards, I would be interested to know what their general strategy, when deciding who gets to be what skin color, was. *(Homer´s (if he existed) version of "Fall of Troy" is about as historic as space thor :>)
The other thing is, that a lot of people base their "historical accuracy" regarding skin color in ancient time on the pictures/movies/stories and so on from the last 1000 years - a time period, where our countries slowly turned all the romans and greeks into 100% european looking white dudes. So now Jesus is white and Santa is White and everyone in the roman empire (which had tons of colors, not just in the lower classes) and their imaginary heroes are white.
A roman watching a movie about them today, would probably wonder what all the barbarians are doing in his city. Thats not historical accuracy thats our ancestors changing the original to better fit their own culture. Which wasnt problematic, when some monk did it a thousand years ago, and its not problematic now, that we changed back to more multicultural societies.