Necro thread but my players may be looking at it so...anyway.
In the mainworlds of the 3I, human ethnic groups are so thoroughly mixed there IS NO WAY TO TELL RELIABLY, visually, someone's background. Even in most cases genetics aren't going to tell you much conclusively.
That doesn't mean there's no difference, however.
IMTU, the Vilani were light-to-medium skintone South Asians in appearance, meaning that in some circles that's seen as an implication of Vilani (high SS/high caste/old blood family) 1st Imperium bloodline.
The Solomani surge was driven by Earthlings long after Terra had largely de-balkanized and intermixed basically randomly (far moreso than today), so Solomani could be literally anything. There have been occasional (and continue to be) "purity" fringe movements for literally every single ethnic group generally seen by most societies to be umbrella'd as "Rule of Man Crazies". There are still occasional people you meet who appear a sole ethnic type - sino-Asian, south-Asian, Andaman-African, Nordic-caucasoid, etc forever - but they're *exceedingly* rare now. Humans like mixing. (shrug)
That said, there are certainly REGIONAL ethnic variations and concentrations, having to do with their origins and how cosmopolitan they are socio-historically.
A planet settled originally by colony vessels sponsored by the Azanian Union perhaps 1000 years ago was primarily dark-skinned but over 1000 years of interaction is going to be more or less mixed. If they were red-zoned and insular, they might still be fairly (a little shockingly to 'modern' sensibilities) ethnic.
OTOH, The starport governor maybe "militant pureblood Azanian, excessively proud of her heritage' named Motsuhiko Ling-Park and be fair-skinned redhead with freckles. People today truly don't see any connection between skin tone, politics, culture, etc.