Looking at the actor’s CV, you wouldn’t have expected to find her in this sort of R-rated project. The Westchester native, 26, attended NYU for acting, but in her junior year she was tapped to join the ensemble of Hi-5, an international children’s TV show that still airs in reruns on Discovery Kids in the U.S. From 2002 to ’06, Mosley lived in Sydney for six-month filming periods. She says it was a daunting commitment, but she relished it. “My dream, probably since I was in middle school, has been to do art, travel and teach,” Mosley says. “Suddenly I found myself doing those three things.” When the show went on permanent hiatus two years ago, she returned home, and made her Off Broadway debut in the children’s musical Max & Ruby.

It’s obvious why the producers of Hi-5—an educational mix of animation and pop-flavored musical numbers—envisioned the performer in brightly colored costumes bouncily engaging young viewers: Mosley is delightfully upbeat, with a light, high voice, wide eyes and expressive features.

Moïse can’t imagine anyone else in the role she wrote. “Karla was able to bring something fresh and youthful to her approach to Alphine,” the author says. She also taps into her femininity—a feat that Moïse notes seemed tough for the other black actors who auditioned for the part. “They struggled very hard to perform their femininity,” she recalls. “Not because they weren’t skillful, but because they had never been asked to play a part like this before. Usually, we see a lot of the strong, big-mama characters. Bitchy or sassy.”

Alphine does have bitchy and sassy moments in Expatriate, but she’s a moody, hilarious, loving, flamboyant and rather unpredictable creation. “She’s a whole person,” Mosley agrees. “She’s not just an addict, not just a star, not just an abused child or someone with a high libido. She’s all those things and more; she’s bright, deep and funny.”

The impetus for the drama came when Moïse asked an actor friend what her dream role would be. “She was always in predominantly white ensembles, in what I’d call marginal roles,” Moïse recalls. “She said she was really interested in Josephine Baker. Who are the Bakers of today?” So the playwright invented modern equivalents.

What resulted is a play that is an expressionistic examination of race, showbiz and friendship. Claudie and Alphine are opposites who complement each other; Claudie escapes to Paris to become a lesbian artist; Alphine, sliding into addiction, joins her. The two create a singing act that becomes the toast of Paris. Eventually Alphine succumbs to her inflated self-image. “Karla and I laugh because we’re playing these sexy rock stars and we’re both dorks,” the playwright says.

Nerd she may be, but Mosley might also be kicking off a lively career (she’s nabbed small roles on Gossip Girl and Law & Order). Right now, she’s busy juggling Alphine as a complex, flawed person who still burns bright. As for all the sex, drugs and rock & roll, she is intent on “not romanticizing it. That’s the paradox of addiction,” Mosley muses. “I’ve known many addicts in my life. Some of them are the dearest, most hysterical people I’ve known. They can shine so bright and be a gift to the world—and then they’re gone.” Not something she needs to worry about.

Expatriate is at the Culture Project through Aug 3.