Politically correct or by the book?

One reviewer sees "the hand of political correctness rather than imaginative casting in having the Landless siblings played by black actors".
As I am part way through reading the book I can say that Dickens implies strongly that they are at least part Ceylonese, by several references to skin colour, and of Neville that "There is something of the tiger in his dark
blood."
Dickens' tone is rather of admiration than anything derogatory. Helena is portrayed as both admirable and desirable, though a distinct contrast to his usual "child bride" obsession, which also gets an airing.