Which is one of those cases where the Roddenberry legend is slightly undermined by reality: I'm sure he was a pioneer in wanting to have racial diversity in the Star Trek cast, but he didn't have to fight the network to do it: he was pushing at an open door (so long as they were the support cast, obviously.
...which is why I posted "up to that time"
regarding Hooks from NYPD
and Cosby on I Spy
--they were cast as part of the series leads, which was historic, both predating Clarence Williams III on The Mod Squad
(1968) or Haynes on Room 222
(1969). As African American males, Cosby, Hooks (and Morris on Mission Impossible
) already broke ground, which is why its easy to imagine Don Marshall jumping at the chance to play an important, leadiing role on Land of the Giants
, instead of what would have been an occasional guest spot on ST, and certainly not a character in a position of any sort of authority.