When Steve Sailer said in TakiMag that in spite of Sir Laurence Olivier's sincere attempt to black himself up for the role of Othello, he "just looked like Charlton Heston in blackface", what he means is that Olivier's Caucasian features showed through the makeup at close range.
However, Olivier did make an effort to act like an African.
When two white men, Freeman Gosden and Charles Correll, played black characters Amos Jones and Andy Brown on the radio, in the iconic Amos 'n' Andy show they had no problem imitating what at the time was called "Negro dialect". (I say iconic—but it's been Deplorable for years, of course.)
But when they tried to turn their radio success into a feature film in 1930, it was a miserable failure.
The problem is that that while they could "talk the talk" they couldn't "walk the walk"—literally, in both cases. They sounded black, but they didn't move like blacks.
There's a scene in the 1970s movie Silver Streak in which white comic Gene Wilder, on the run from the police has to disguise himself as a black to get on a train. Below, you see Richard Pryor trying to get him to actually walk like a black person:
It's a success both comedically and as stratagem to get him on the train, but it's Deplorable now, too.
A 1950's TV show of Amos 'n Andy featured actual black actors—but it was taken off the air due to NAACP pressure. (Yes, it's Deplorable, too—a black woman writing on Slate.com called it "infamous".)
You can see what I mean about Olivier, as an actor, moving like a person of African descent here:
In the early 1960s both Gielgud and Olivier played Othello for the first time in their careers. Gielgud spoke the verse with his usual music, but he was physically and vocally too light to play the warrior credibly. Olivier lifted weights, deepened his voice, and played the noble Moor as a wildly jealous African. It was a complete misreading of the play, but it was electrifying.
You can watch the whole thing below—it's the last time, apparently, that it's going to be done by a white actor.