My college roommate and I were watching Deep Space Nine, and in the episodes a small group of Bajorans were meeting with Cmdr. Sisko. One of the leaders of the Bajorans was played by a black actor.
"That's cool," my roommate said, "They have African-American Bajorans." Then after a moment he said, "Of course, that's inaccurate. He's Bajoran. Bajor is a different planet, there's no Africa, there's no America."
Over the course of the series, we saw that the Bajorans were as racially diverse as humans are*, but we never learn any real details of that diversity. And that's fine, because it didn't need to be directly addressed, it just was a part of their reality, easily achieved by color-blind casting.
Writing different races in secondary world fantasy, though, can be a challenge. And I'm not even talking on a cultural level, though that's definitely an aspect. I'm talking about purely on a level of clarity and description.
Here's the exercise: describe a character whose race is different than the norm of the primary culture of your world, without using any geographic or geopolitical signifiers from our world. Also, avoid words or terms that could be racially charged. Now do five more.
How do you feel about what you did?
Now, one thing you can do is make distinctions between races and cultures in your world without getting too specific, and noting how the characters are aware of the cultural differences themselves.
"You reek of fish, you know," she said, her flat nose crinkling in disgust. Kaiana Nell was a dark haired, brown-skinned girl. Ruder people would call her a Napa: half Druth, half Napolic. She was a soldier's daughter, born out on the tropical islands during the Fifty Year War.
Ruder people would call Veranix a "Dirty Quin" if his Racquin heritage were as clear on his face. Of course, Racquin were only a little darker than 'regular' Druthalians. They just kept to the roads and kept to their own, for the most part. Though Veranix, like Kaiana, was only half. His father was a 'regular' Druth, born and raised in Maradaine, just blocks away from the University. Veranix had inherited his father's fair skin and green eyes, and could speak in his father's Aventil neighborhood accent. No one suspected he was anything but a local.
Did I hit the mark, or did I miss it? Perhaps badly? I think I've still got room for improvement.
But who doesn't? Even George R. R. Martin has left a lot of room for interpretation. It seems every time a new character is cast for Game of Thrones, I see intense debates on how the actor or actress does not match what various readers imagined for that character or that character's race.
*- Which makes a strange sense, in that-- save for their nose ridges-- Bajorans were indistinguishable from humans in appearance. If you can accept that premise (as a time-and-budget saving reality on a TV show that couldn't hire actual alien actors), the rest follows.