To be brief. Hair is one of those details that sometimes get's over looked when talking about ancient cultures. I was reading some alt-history earlier and I really appreciate that David Drake and Eric Flint took the time to get the details of hair right in the different members of a diplomatic party from the Auxumites which include an African citizen (who announces himself as a slave but it becomes rapidly clear it's not a simple relationship). So. I'm not demanding to see evidence you're artists have looked into this as I have seen the culture cards online and from the open dev sessions. But I kind of remember the diplomatic representative primarily only had changes in their clothing, not necessarilly hair, tattoos, or, piercings. Obviously I can appreciate it being a somewhat minor priority in the scope of all that exists, but, I love the idea that with more details Humankind will help to show off the rich diversity of cultures and peoples.

Personally, I'd like the ability to change hair and skin colour between ages. I know that sounds strange about the skin colour, but I would feel a bit weird about playing a white person in any of the bronze age and most of the classical age civilisations, partially because you can clearly see the skin colour of all their units.

I presume then also skin tone doesn't change with cultural choices? I'm not objecting. But I am curious. As mentioned in the book I'm reading one of the diplomatic members from the Auxumites was an African so it's not like it'd be impossible your representative could be a different ethnic/culture/skin-tone than your current culture. That might also be quite a bit of work and maybe more open to problematic interpretations. 

Since the Avatar represents you the player just as much if not more as it represents a "personification" of your people's cultural identity, the avatar itself does not change during a game and is not tied to the culture you're playing. Only their clothes change based on culture.