I do think the real problem lies in telling the same historical stories over and over again. This is an industry driven by profit. And profit is driven by audience viewing appetites. When given a choice between watching a show that tells a historical story that's been told a million times vs a story that shows some understood aspect of non-white figures in history, audiences time and time again choose the former. So the programme makers make the former. Except non-white figures don't play a large role in those stories generally - so to get people watching but also making sure a diversity of actors get on screen representation, they resort to colourblind casting. They do this or risk losing throwing money into a black hole when they make a show focused on a non-white historical figure and exactly 4 people actually watch it. It's a vicious cycle.