I guess it'd depend on how accurate it really was. If there honestly were no, say, black people around, then that'd be one thing. But if, for example, Skalitz historically did business with Algerian traders or whatever, I could see saying "There should at least be other people around who are people of color." I dunno. I think people's perceptions of history, though, are often not actually that historically accurate and they might be surprised to learn that history was different. Surprised enough to just reject it out of hand in some cases.
I think you can choose artistic reasons to cast someone else who doesn't fit that bill. It depends on what you're trying to do with your story and why you're trying to do it. But let's also not pretend that Hollywood gives a damn about historical accuracy when it almost never does.
I've posted about this before, but the TV show Vikings -- which aired on the History Channel -- was wildly historically inaccurate, and not just because it's based on sagas which are themselves of questionable historical accuracy. I'm talking, like, "Nobody really opened a book about this, did they?" levels of inaccuracy.
Examples: They make it seem like the Norsemen of the late 700s knew nothing of England, when they had already been trading with England for some time. Now, maybe we can excuse that as "Yes, but these specific Norsemen have no idea what England is," but it's still a stretch.
The Jarl of Ragnar's town gets pissy when the guys sail off, and summarily maims a blacksmith. In addition to this being like intentionally trashing the ONE factory that makes cars for you (blacksmiths were skilled labor back then), jarls had nowhere near that level of authority in Norse culture, which actually operated in a quasi-democratic fashion more often than not. Yet they have this guy acting like a generic feudal lord who can do whatever he wants with impunity. Not remotely accurate. The outfits tend to be inaccurate, too, nobody wears a helmet, etc., etc.
When they land in England, we're shown King Aella of Northumbria as one of the first English monarchs (heptarchs?) reigning during that era. Later, the main characters engage in the famed raid on the Holy Isle of Lindisfarne. So, what's inaccurate about that, you ask? Well, nothing, as long as you'd also be fine with a film that depicts Abraham Lincoln signing the Louisiana Purchase, or a story involving, say, JFK winning the presidential election of 1892. Aella ruled from around 862 until 867 when he was killed by Ragnar's ADULT sons. The raid on Lindisfarne happened some 70 years prior. It'd be like having Chuck Berry play Johnny B. Goode for Queen Victoria. But, of course, nobody cares because, whatever, it's just a show, it's just meant to entertain.
If you actually know anything about this era of history, it's glaringly inaccurate. But people don't, and so they don't care. And, I guess, why should they? Vikings is still a really fun, entertaining show, it's just...you know, not really historically accurate at all. But even if you do know about the history, it's ultimately not that big a deal when you just settle back and accept that this is gonna be an historic-ish show that's more about cool action than accurately portraying history.