"American Idol" contestants Pia Toscano, Hayley Reinhart and Lauren Alaina wear Gwen Stefani's L.A.M.B. designs. Photos Courtesy: Fox

Rock night on "American Idol" produced some unique musical and style notes for its three remaining female contestants as singer and fashion designer Gwen Stefani performed the role of guest stylist.

Stefani outfitted Pia Toscano, Haley Reinhart and Lauren Alaina head-to-toe in fashions from her L.A.M.B. collection, giving the show's ladies costume designer, Soyon An, a sweet escape from her normal duties.

Stefani went heavy on rock-steady black-and-white and added towering, edgy footwear from her accessories collection. The new face of L'Oreal Paris even had a say in the contestants' hair and makeup styling: Notice the slight, Stefani-style pouf in Toscano's ponytail and the Harajuku Girls-inspired matte red lips.

"They were like mini Gwen's," An says. "They loved working with Gwen and thought she was the sweetest."

An gave us the behind-the-seams dish on each contestant's "Rich Girl" moment:

Pia Toscano: Her strapless, animal print L.A.M.B. jumpsuit was a modification of a look Stefani wore at New York's Mercedes-Benz Fashion week in February. Its "very Gwen" wide-leg pants were a style departure for Toscano, who also took a performance risk, stepping out of the ballad zone to sing Tina Turner's uptempo "River Deep, Mountain High."

An, who has been styling Toscano in series of diva-glam dresses, was all about the singer's coiled, steel Cleopatra-esque choker. "That was my fave. It kind of brought out the Tina Turner in her. Don't you think?" The print "and Pia's voice brought the edge and sexiness to the performance."

Judge Steven Tyler was more than a little impressed: "There's a million guys out there in a million bars having a million drinks about you tonight," he told Toscano.

Haley Reinhart: Her form-fitting leather pants were An's favorite look of the night. "I LOVED them," she raved. Also a hit: The way the fringed-panels on the bottom of the belted black-and-white plaid top "brought out the Boho" in husky-voiced Reinhart as she sang Janis Joplin's "Piece of My Heart." The look also proved that "plaid doesn't have to be preppy."

Lauren Alaina: The country-singing teen's gingham bandeau L.A.M.B. top was paired with coordinating short-shorts, black boots, opaque tights and a fitted tuxedo jacket. "This was a very fun and flirty Gwen look," An says. Why the combo works? "You can tame prints with a solid jacket for a finished look."

For more "Idol" fashions, read about the styles An put the ladies in for Motown week.

And read what Stefani had to say about her vanity in Elle's recent "Women in Music" issue.