Old Academy Players’ Philadelphia premiere of Lori Sigrist and Joe Simonelli’s “A Rainbow Holiday” brings out the best elements of the play, an homage to cultural diversity set on the day that symbolizes family togetherness - Thanksgiving.

The opening scene immediately introduces the core conflict. Maggie (Mary Waterfield) agonizes about the upcoming Thanksgiving dinner with her live-in boyfriend Jerry (Guy Sims).  She had invited her gay son Adam (Daniel Mendoza) and his boyfriend Adam Kent (Micah Wagman) to the feast. Now she learns her born-again Christian daughter Alison (Natalie Merlino) and husband Dan (Chad Curtis) also plan to attend.

Terri Fries Bateman directs the proceedings and also designed the set, a stylish living room with restful coloring markedly at odds with Maggie's distress. The guests are a combustible mix of conflicting values. Maggie drinks heavily as she paces around the dining table, venting her unease to amiable Jerry. But she cannot gain peace of mind.

Son Adam and his boyfriend are the first to arrive. Maggie and Jerry welcome the gay lovers. They sit comfortably on the living room couch and chat. The couple lives and works in California, where they bought a house. They traveled across the country just for this annual Thanksgiving dinner.

Tensions ratchet when the churchgoers show up. Alison subtly disapproves of her mother's drinking and her living with Jerry outside of marriage. You expect a more overtly volatile reaction when she learns about her brother's new way of life. At first, Adam tries to dodge the conflict by introducing Adam Kent as "a neighbor."

Julie is the last to show up. She is Jerry's daughter and her attendance at the Thanksgiving celebration was not expected to cause concern. But Julie is in agony over her husband Mark. She has discovered his secret cell phone and learned he is having sex with other women while pretending to be working late, or playing poker with the boys.

Hannah Leifheit's portrayal of Julie is the highlight of the show. Tall and lithe, she moves gracefully about the stage like a dancer. But the character's distress shows up in the shifting cadence of Leifheit's voice and the tortured expressions that cross her face. When Mark (Jamaal White) finally arrives the table has been set.

Seated for dinner, host Jerry says a humorous grace before the meal that lacks piety. Offended, Dan steps in to praise the Lord, while Mark sits apart from the table to check his cell phone and Julie stares into space.

Playwrights Sigrist and Simonelli argue for tolerance and cultural inclusion. To that end, the contending parties patch up matters. Dan talks to Adam Kent alone in the living room. He is troubled when he realizes that he likes the man even though Dan realizes Adam is gay and does not believe in Dan’s God.

Similarly, the other Adam meets his sister in the attic where they used to play as children. They go through a cardboard box that holds their childhood playthings and reminisce about their experience of growing up together.

In this way, they come to accept the different life choices they have made.

But the ease with which these contending couples arrive at a live-and-let-live solution feels formulaic. The cast is capable but the script does not give the characters notable action or dialogue. They are like stick figures in a morality play and the playwrights lay it on with a trowel when a rainbow ends the play-long thunderstorm.

You do care about Julie. She stars in several scenes, agonizes, makes discoveries, takes action and changes. The script allows Hannah Leifheit to create an authentic character. Jamaal White, too, is an arresting figure as Julie's disturbed husband. You are affected when Mark shows up at the end to plead for another shot at marriage.

Will Julie accept his plea for another chance? Or will she walk out like Ibsen's Nora to start a new life and face an uncertain future? It is a tad melodramatic, but they seem like real people. Their troubled relationship is engaging and becomes the major strength of the play.

This relationship is also the play’s weakness.  While Sigrist and Simonelli toss in some humor ---- as when Jerry stalks philandering Mark with a rolling pin ---  "A Rainbow Holiday" is essentially didactic. But with so little vitality in the main characters, the playwrights resort to peripheral drama to hold your attention. The lack of empathy for a man too troubled by an addiction to abide by the norms of marriage is curiously out of step with the play's sermonizing about the need for tolerance and forgiveness.

"A Rainbow Holiday" runs through Nov 17. For tickets, call 215-843-1109. Old Academy Players is located at 3540-44 Indian Queen Lane.