The hardest thing about writing in a secondary world where there's no Asia, Africa etc., when I'm not shooting for a
fantasy counterpart culture approach to my world building, is also not falling into the "ambiguously brown or olive skin" trope. I have one character who looks like he's from east Asia (if he were from our world), one who looks like she's from India, or possibly the middle East, and one who is of mixed ancestry, one parent from the same country as the previous character and one from an area where people look more European. All three have dark brown hair and eyes and skin that falls on the olive to light brown spectrum, yet they're not the same racially or culturally.
Aside from introducing their countries of origin and their different cultural norms as early as possible, and differentiating skin tone a bit (amber/tawny, light brown, and olive), I don't really know how to describe their features so the reader gets a clear image of their racial features aside from the "
ambiguously brown" trope. I mentioned long eyes for one of the characters, but I don't even know if most readers will know what that means. One thing about the old "almond eyes" descriptor, inaccurate and cliched as it was, it immediately told readers that the character in question looked like he or she came from Asia.