The Color Purple is a musical with its own mandate: empowerment for the underprivileged, whether black, homely or female. It certainly celebrates that, and with the arrival of a true American Idol in the leading role, it may even come closer to making good on that promise.

Alice Walker’s novel is by now a classic of its kind. The musical — less good than the novel of the same name but better than the movie — is the rare Broadway show that elicits not merely a standing ovation at the end but also one along the way. And even if you are not black, homely or a woman, you join in with your heart, if not with your feet.

It concerns good but hapless Celie, the sweet, uncomely sister on whom every possible torment is inflicted — from incest to wife-beating, from a father who begets children on her only to give them away, to a mean, loveless husband who treats her as an abused slave. The one being she loved and was loved by, her pretty sister Nettie, is snatched from her by missionaries.

It is also about how, slowly but very surely, every conceivable good comes to Celie, till in the end her cup runneth over with achievement, affluence and universal affection. It is a fairy-tale musical that, like its heroine, works hard to earn every bit of the good feeling it elicits.

This is, largely, the accomplishment of the new leading lady, Fantasia. Unlike the role’s creator, La Chanze, Fantasia is neither pretty nor dainty. But, in her first stage appearance, the plain and chunky 22-year-old acts up not only a storm but also the deepest feelings with the mere rolling of her eyes.

Yes, she won American Idol, became a hit recording artist, published a best-selling autobiography and starred in its TV-movie version. But would that guarantee easeful dominion over a stage musical in a lead not tailored on her? She does it all, including convincingly aging in a role that extends from 1909 to 1949. Fantasia’s inner beauty and innate acting talent achieve wonders for the show and creates a transporting experience for the spectators.

True, there was good all along in Marsha Norman’s book and the score by Brenda Russell, Allee Willis and Stephen Bray. Even better were the thrillingly shape-shifting sets by John Lee Beatty, the grandly gaudy costumes by Paul Tazewell, the penetratingly enhancing lighting of Brian MacDevitt and Jonathan Tunick’s incisive orchestrations. Also the polymorphic choreography of Donald Byrd and sure-footed staging of Gary Griffin.

But it’s Fantasia who makes everything click gloriously into place. Unstinting praise, too, for the cast, which is largely new.

The Color Purple is playing at Broadway Theater, Broadway at W. 53rd St., New York City. (212) 239-6200.