I think what was done with The Railway Children illustrates both the potential and the limitations of trying to make history in historically-very-white countries look more multicultural.
The Railway Children used a cast with people of various colors, and did not go for a color-blind approach; the film actually did take a realistic look at what it was like to be a black guy in the UK and US at that time, and by all accounts did a pretty good job of it. And it certainly can't be accused of lying about the past (which is the complain that several people, including me, have made about the "stick some random non-white people into a George Elliot production etc.") or pretending that people in 1940s Britain/America were race-blind post liberals.
But this approach is also limited in each nature. It makes The Railway Children into, to an extent "a film about racism."
That's not a bad thing in itself; there should be some "films about racism."
But do we want every costume production, or most costume productions, to end up having to be "about racism"? Are they all going to have to end up having a "Racism Issue" thing inserted into them, or else be considered unmakeable or unwatchable?
Because that's another issue which is causing some annoyance and frustration among viewers: the perceived sense that films and TV in the last decade or so have acquired a preachy feel, that they keep bringing in the same agendas again and again etc.
I do feel a bit puzzled by the "perceived scarcity" that seems to exist when it comes to non-white characters in children's TV and film. I have Netflix: if I open up to the Kids page, take a flick through, most of the productions have casts featuring children of different races, which for modern productions is exactly as it should be: this is not the 1980s, after all, and we've moved on massively since those days.
Is it really too much to suggest that we just allow 1940s (and earlier) Britain to be portrayed "roughly" how it actually was in those days, for the small number of productions that are actually set at this time? We're literally talking about the odd film or TV series that forms a small % of the total content that kids watch. Is watching the occasional film with an all-white caste honestly going to give the kids cooties?