The abstract painter Stanley Whitney — known for his signature grids of bold color inspired by jazz, American craft quilting and the midcentury Color Field artists — has been making art in New York for more than 50 years, but only in the last decade has he attracted widespread attention from curators and collectors. One of those collectors is the Broadway theater director Joe Mantello, who moved to Manhattan in 1984. While Whitney, now 72, has plied his solitary craft since his own arrival to New York in the late ’60s — not quite fitting with more overtly political black artists or the white male-dominated Expressionists — Mantello, now 56, blazed through the city’s theater scene, first as an actor (in 1993, he originated the role of Louis in Tony Kushner’s “Angels in America” on Broadway) and then as a lauded director of shows ranging from extravagant musicals (Stephen Schwartz and Winnie Holzman’s 2003 “Wicked”) to seminal gay plays (Terrence McNally’s 1995 “Love! Valour! Compassion!”) to popular revivals (last year’s production of Edward Albee’s “Three Tall Women”). This month, he brings Lucas Hnath’s obliquely political comedy “Hillary and Clinton” to Broadway...