* THE HEIRESS (Cort Theatre): Several cast changes have occurred in what was the single best production of last season, although Tony Award-winner Cherry Jones is thankfully still playing the title role, and Tony nominee Frances Sternhagen also remains. Donald Moffat now plays Dr. Sloper, bringing more elegance and slightly less ferocity to the role than Philip Bosco, he delivers a skillful and somewhat more sympathetic portrayal. Michael Cumpsty, who now plays the fortune-hunting suitor, is even better than his predecessor. This play provides a feast for actors, and will prove a showcase for even more great performances in the future. * BLUE MAN GROUP IN TUBES (Astor Place): Hard as it may be to believe, this bizarre performance group is now in its fourth year Off Broadway, and a second production is opening in Boston this October. The original members of Blue Men Group have left the show and are developing new material; their well-trained replacements are filling in nicely. ''Tubes'' has become one of the most popular tourist shows in New York, and a second viewing reinforces the reason why: It's witty and post-modern enough for sophisticates, and silly and goofy enough for kids. Just be sure to wear old clothing if you sit near the front; you're likely to be splattered with any number of gooey substances. * FOR COLORED GIRLS WHO HAVE CONSIDERED SUICIDE WHEN THE RAINBOW IS ENOUGH (Tribeca Performing Arts Center through Sept. 24): A 20th-anniversary production of Ntozake Shange's groundbreaking, highly choreographed, theatrical poem about the state of black women in America. It's directed by the author herself and performed by a cast of seven talented actresses who provide a raw, blazing energy. The show is less dated than you might expect, and provides a sad reminder that in many ways things haven't changed in the last two decades.