Not just Uhuru, the regular cast also had Japanese, Russian, Scottish and of course Vulcan characters.
Hard to realise the significance of a Russian character as one of the good guys at the height of the cold war.
And then of course you had episodes that were dedicated to condemning racism, such as "Let That Be Your Last Battlefield" where the aliens were half black, half white.
And of course having Kirk and Uhuru kiss was quite literally "pushing it in the viewer's face", at a time when segregation was still an issue in some US states.
If you have a problem with diversity in 2018, you are an asshole.