I feel extremely gratified to have stumped the bottomless well of knowledge that is HHW. Here are the answers:
The musical: House of Flowers
The legendary star: Pearl Bailey (don't quibble, darling, she was a legend in at least her own mind), who would go on to star in Hello, Dolly!, which made history by being the first then-currently running musical to continue its run with an all-black cast
Supporting Cast #1: Ray Walston, who left this show for his Tony turn in Damn Yankees
Supporting Cast #2: Diahann Carroll, who won her Tony for No Strings, a show with unusual elements including: 1) an interracial romance; 2) lyrics by Richard Rodgers; 3) orchestra with no strings; 4) orchestra onstage
Supporting Cast #3: Geoffrey Holder, who won his Tony (directing) for The Wiz, which like the Dolly! recasting was an all-black musical (and also, stretching a bit, based on an all-white musical, though that was a film).
TV Credits: Walston in My Favorite Martian; Carroll in Julia; Holder in 7Up commercials
Yes, I have entirely too much time on my hands today. I've tried washing it off, but it's stuck (not in SF).