Lauren Alaina. Photo courtesy of Fox

Haley Reinhart and Lauren Alaina got to voice their true fashion personalities for a freewheeling "American Idol" competition night devoted to songs of the 21st century.

Ladies costume designer Soyon An went for a '50s pin-up girl vibe with jazzy Reinhart who vamped in sexy, red polka dots, while teenage Alaina got to play "cowgirl princess."

The stylist also had an unexpected sartorial challenge: some of this season's eliminated contestants, including fashionable Pia Toscano and Naima Adedapo, made a surprise return to the "Idol" stage to perform Pink's rebellious "So What." Their return meant an emergency shopping trip for piles of edgy black clothes.

Here are some of the fashion high notes from last night's show:

Reinhart: "We're teaching fashion history with a modern twist here on "American Idol,'" says An, who explains that the husky-voiced singer likes to channel a sexy '50s siren when she sings in her signature, bluesy style. So for her interpretation of Adele's "Rolling in the Deep," An chose a red polka dot dress from Stop Staring, adding towering nude Guess pumps and accessories by Bijou Tresor.

Haley Reinhart. Photo courtesy of Fox.

Alaina: After back-to-back performances dressed in black, An wanted her "to get back to her cute country self." For her performance of Sara Evans hit "Born to Fly," she dressed the 16-year-old in a blue skirt with hem-line embroidery detail by Wet Seal, an embossed Guess by Marciano white T-shirt and Guess denim jacket. Necklaces featuring birds and butterflies from Guess and Wet Seal --to signify the flying theme--along with a pair of Boot Star boots finished the look.

The Rest of the Crowd: It's unusual for "Idol" to give its stage back to eliminated contestants before the season finale concert and An only learned late Friday she had a big cast to dress again. "I had to shop for them and fit for them on Monday," she says. "They each had their own uniqueness and I went with that."

Highlights of their ensembles included Toscano's sexy, black-fringe-trimmed halter from Bebe: "Their collection right now is hot," says An. Jones' interesting chain-accented vest was by Amalia Mattaor.

StyleList loved the styling trick An employed with Megia: A flirty, black-fringed skirt was pulled over a basic dress to give the look more edge and movement.

Speaking of modern pin-up girls: Check out one of our beauty writer's cosmetic experiment with the look.

Eliminated contestants, from left to right: Karen Rodriguez, Ashton Jones, Paul McDonald, Pia Toscano, Naima Adedapo, Thia Megia. Photo courtesy of Fox

And for more "Idol" fashion scoop, read last week's fashion recap.