> What's your source for the claim that a typical Roman citizen is white? That's a pretty bold statement. Much bolder than the relatively non-controversial statement that Rome had a diverse population.
We're circling back to the definition of "white". How's that a bold statement? Today's Great Britain has very diverse population, too, including lots of people from Africa, and yet I wouldn't think that a statement that a typical Brit is white is controversial. Typical Brit is not black, although there are many black British people, of course. And even if we constrain discussion to the most narrow definition of "white" (say, 18th century Englishmen) let's not forget that English people are the result of centuries of mixing of Britons, Germans, Celts... So, white Britons are themselves of diverse ancestry, but all these diverse ancestral people are "white". Let me repeat that race is an artificial construct, but if I'm pressed to say if someone is "white" or "not quite white" I can only go by outside appearance. Someone in Europe can have some genes from one Zimbabwean ancestor, but if he "looks white" to me, I can only say he's "white".
> The problem is simply with depicting all of Rome as (essentially) British.
Yes. That is a TV series. The point of TV series (in my opinion) is not to be 100% accurate, it's to entertain and (somewhat) educate. And the people in TV series are not real ancient Romans, but current actors. The series is for British audience, so it's normal that it's filled with British actors. If the series was produced in Bulgaria, the senators would be played by Bulgarian actors. Both are not exactly of the same color spectrum as ancient Romans, but are close enough to pass as Romans to their viewers. If the series was produced in China, and Romans were played by Chinese actors, that would probably pass as normal to Chinese audience. Maybe Zimbabwean actors could pass as Romans, at least in sub-Saharan Africa; why not? I'm not sure why people insist so much that British actors are bad representation of Romans. They seem quite OK to me (I'm not British).