Clear political correctness to add in more poc.
Of all the things Bioware has done to the Dragon Age franchise (especially Dragon Age 2) this is somehow a point of contention?
Was it weird that your Cousland in the Human Noble in Origins could be black and not look at all like your mother and father? Yes, yes it was (barring possible genetic boomerang or adoption). They fixed that quibble with Hawke's family because now they are based on key player decisions when modifying character features. Outside this single scenario, there is no cause for such arguments.
Otherwise, there is nothing wrong or historically inaccurate about multiple ethnic groups coexisting within a single local even during the middle ages. Although in the Dragon Age setting it appears that the elves faced the brunt of the racism, and we are likely in the Late Middle Ages - maybe just before the Renaissance.
Between common migration and intermarriages among houses of nobility across the continent there really is no reason why skin tone should be allocated to only a few specified groups. Besides, plenty of portrayed Tevinter are not like Dorian - it's just that not all are pasty mages with close-cropped family trees like the European Hapsburgs. Maybe Dorian has some Antivan in him, or he could even be distantly related to the famous Rivaini Queen Asha Campana. But I don't think they actually are "swarthying" up Tevinter so much as just making interesting characters.