And these groundbreaking actors were usually described as "the black guy" at the time.
Or more impolitely, "the token black guy".
I don't think that's fair. Many of them were far more than tokens. Heck, of all the main-cast black characters in '60s TV, I'd say Uhura was the most tokenish, because she never had a focus episode and rarely emerged from the background. Cosby's Alexander Scott in I Spy
was a completely equal lead to Robert Culp and was always treated with dignity; he was the intellectual while Culp was the athlete. (Ironically, the 2002 feature version with Eddie Murphy playing Culp's character -- and changing him from a tennis pro to a boxer -- was far more racially stereotyped than the '60s original.) Barney Collier in Mission: Impossible
was far from a token; he was a brilliant engineer who was often the linchpin of the team, growing only more important as the series went on, and he had his share of episodes where he was the featured character. Don Marshall's character on Land of the Giants
was also a nicely non-tokenish role, treated no differently than the other male leads.