Both DAO and DA2 are known for having game engine issues with regard to dark skin tones and it was a limiting factor, yes.
However, there are times when the developers just sit back and say, "Look at some of these crowd shots. Why are all the faces white?" and then make adjustments. This happened in DAI as well with female characters. In this case, DAI was also aided because the Frostbite engine was just better at making dark skin tones.
oh really 
http://vignette4.wik...=20100405005711
and they have no problem in Kotor and Neverwinter too
let be honest they does not have those and never think as never have explanation to add darkskinned humans, rivaini as antivans and some tevinters humans was tanned and thats all, every tanned human was from a north or corcari for those who live in south lands, they never have darkskinned ones and it was by the lore that all human race was arrive in Thedas from a single source and later they spreads in Thedas
the only darkskinned race was a kossiths/qunari
it is not a matter of engine, they never have those in art and concepts as lore, and yeah bioware just add something for a presentation and "fill a quota" thing
they add them only after some peoples start to complain that they does not show them so we have them in DAI and only Vivienne(who originally was a blonde pale evil mage with poisons and politic assasination) at least have a official rivain origin, with others it was just "change someone so they would have a darkskin and do not care about some lore, biology, logic and sense...all what is matter that we do not hear about that we do not have darkskinned humans in game"