After this, I made sure I had BBQ for lunch the next day (and regretted that I now live in the Midwest instead of Texas), but I also got down my copy of some of my Iron Kingdoms source material, notably the IKCG or Iron Kingdoms Character Guide and the older Lock & Load: Iron Kingdoms Character Primer both of which discuss the various human ethnicities in the Iron Kingdoms. In the larger IKCG, they are illustrated--a sample bust type portrait of a man and woman of each race. In the L&L book, they are described physically. Curiously, you need both books to get a complete picture of what a "typical" member of each ethnicity looks like.
After that, I also checked out my Pathfinder Chronicles: Campaign Setting, the guide to Golarion, and especially the Inner Sea region. Both books do a pretty good job of describing human ethnicities and making them interesting choices to pick in play. The Iron Kingdoms takes the dubious step of creating mechanical differences between them, while Pathfinder instead has "half feats"; traits that are based on either culture, country, or environment of origin, which also serve to give some cultural flavor to the various human ethnicities.
Not that other settings don't have ethnicities, but these two do a particularly good job of integrating them. Others, like Forgotten Realms, or Eberron, for example, tend to come at us with the overly simplistic Belgariad model, where cultures and countries are 100% mappable, and individuals from each are a caricature of their cultural traits. No, the real world is more subtle.
There are two ways to approach ethnicities in roleplaying games. Pathfinder, for example, tends to paint with a pretty broad brush. Their ethnicities are like Garundi, which make up the majority of the ethnic make-up of an entire continent. In real world terms, that would also be applicable to DARK•HERITAGE, that would be sort of like making "Mediterranean" an ethnicity, and brushing together whatever differences there may be from someone from Barcelona, Nice, Venice, Sicily, Crete, Malta or Tunisia. For my purposes, that's clearly too coarse. But I don't want to go to the other extreme, where I'm saying that even within Greater Catalonia, for example, Valencians, Andorrans and folks from the Balearic Isles are different ethnicities. In real life, there's actually controversy over issues like that.
The genesis of an ethnicity is also a complicated issue. Not every ethnicity is made up of an ancient population core that has persisted for generation after generation after generation for thousands of years (although some are.) Sometimes ethnogenesis requires only circumstances that cause geographically proximate peoples, regardless of origin, to see each other as "their people", to begin to (if they aren't already) interbreed with each other, and to develop common culture, language and traditions. This can actually happen fairly quickly in the right circumstances, and some ethnicities in DARK•HERITAGE are really quite young, all things considered. Others are suitably ancient.
So for DARK•HERITAGE, I'm looking for an approach that is broad enough, yet not too broad. An approach similar to that taken by the Iron Kingdoms, actually. Here's the ethnicities of the setting, speaking broadly: