It depends, magic and magic tech exists in this world so that explains to the audience why people can do weird magic, that’s the suspension of disbelief, you’re being asked to accept the premise that magic is real in this world. The humans of the eastern kingdoms evolved, from the Vrykul who are based losely on nordic peoples from the snowy north. We as the audience know why humans have different pigmentation in their skin, it’s functionally how sunny was it where you ancient ancestors came from.
If you’re on a continent where people evolved to be white, it’s very odd to have black people there. The same if you’re on a continent where people evolved to have an increase in melanin then it would be odd to see white people. You would need to establish connections between these two continents/regions where people have travelled between these two locations. So unless you create a more tropical kingdom in which 100’s of thousands of years ago some of the early humans where also somehow sent, and everyone is black there. Then you would in game need to explain how this long lost continent some how had people migrating about, then it make sense as to where the black people came from in game.
Diversity is good as long as it’s not done at the expense of the story.