Was watching a UK docu called "Bring Back Star Trek" when I heard the ugly remarks.
Whitney struck me as a VERY bitter person. Watch the interview for yourself and see if you can detect any bitterness, envy, and/or racist tones. I sure as hell did.
(So bitter, in fact, that she outright SAID to the interviewer that the show "Ruined her life", and she hit the bottle, hard, for many years after.)
Oh - And along with the 'black' remark, she also called Nichelle's part on the show a 'glorified extra'.
I saw that show too - it was far less awkward than Bring Back Dallas, which ironically, they did, so go Justin!
But you shouldn't view those comments as her only word on her Trek experiences as she was accosted by a mad Bristolian in a mall. She's been a lot more candid in other interviews, her comments were no doubt edited down, and most of the cast haven't had universally wonderful things to say about their time on the show either.
It's also probably fair to describe Nichelle's role as a 'glorified extra' at the time Grace was in the show as Grace had roughly equal billing with De Forest Kelly at that time while Nichelle was a day player. Uhura did benefit from Rand's absence and rose to greater prominence as a result, although actually some of Uhura's best scenes are also in those early episodes.
Most of the yeomen in TOS were little more than eye-candy, although some weren't bad in a fight. It's shame that Grace was treated so badly; I'd have liked to have seen her reprise her role in a few guest slots. She quit drinking after TMP but who knows, maybe if she'd had a role in the Tribbles episode she might have been asked back a few more times and regain a little more prominence in modern Trek lore.