Suskin and The TheaterMania Guide refer to it as a musical about underprivileged ghetto kids, although Walter Kerr is more specific, describing the kids as 8 black and 4 white. I should have checked before posting because the music, lyrics, and book were written by white guys. The critics were pretty hostile, except for Clive Barnes of the Times, who gave it a rave. Suskin liked it too. Apparently audiences took to the show. It turned a small profit. I vaguely remember it growing up, but never bought the LP.
As a kid, the musicals I thought of as black were Porgy and Bess, Hallelujah, Baby! and Purlie, all of which were also written by white people. What did I know? I was just a Polish teenager who liked Broadway musicals. Fortunately I was also a pretty good athlete (football and baseball). Otherwise the neighborhood tough guys I hung out with would have kicked the shit out of me. I always had to hide my Streisand and Garland LPs whenever they came over to my place to watch the White Sox or Bears on TV.