With just a week to go before the "American Idol" finals, Lauren Alaina and Haley Reinhart dressed the diva part of singing superstars while staying true to their musical roots.

Alaina caught the judges' eye with a shimmery blue strapless gown that had Steven Tyler remarking she looked "like she belonged at the Grand Ole Opry."

Reinhart was blown by a wind machine in a flowing, boho ode to Stevie Nicks.

"Idol's" ladies costume designer, Soyon An, took StyleList behind-the-seams to discuss the fashion high notes of the semi-final marathon.
Lauren Alaina: The 16-year-old got a chance to break in a pair of white, bedazzled Neon Dirt cowboy boots she had been begging to wear on stage to sing Faith Hill's "Wild One." "We went for the cowgirl princess look. It felt like it was fun, young and kind of flirty like a country, wild dessert flower," says An. Her coral color-block top was from BeBe, her jeans and belt were by Guess and SoHo Hearts created her blossom earrings.

Alaina wore a sweet but formal Betsey Johnson two-tone dress, with a black sequined top and flouncy skirt, for her second performance of The Band Perry's "If I Die Young." An added Michael Kors heels, Bebe earrings, a layered Guess necklace and rings by Flirt and Danielle Stevens to finish the look. "I wanted to incorporate the literal verses of the song, which mentions pearls and roses, so I did that with the jewelry," An says.

Alaina also provided some live fashion drama when she shared that she ripped her pantyhose right before stage time and a makeup artist worked shimmering bronzer into her legs. "Normally, I've got two or three pairs of hose waiting for an emergency, but she was in a hurry. I just screamed for makeup to hurry with some bronzing cream," says An. "It worked!"

Alaina's third dress, chosen for her performance of Lee Ann Womack's "I Hope You Dance," was sourced from The Mint Collection in Los Angeles. Her accessories included a Guy and Eva bracelet and BeBe earrrings. The floor-length strapless gown featured silver thread woven throughout the baby blue fabric. "When Steven Tyler said that dress made her look like she belonged at the Grand Ole Opry, I knew we got it right and it gave her her moment."

Haley Reinhart: The bluesy girl from Chicago rocked out to Led Zeppelin-- accompanied by her dad on guitar-- in a short, fringed leather halter dress by Catherine Malandrino which An sourced from L.A'.s Kitson boutique. " She wanted to be very rock 'n' roll for this, but I also wanted to keep her look consistent, showing off her legs and her arms, which we've done all season."

Reinhart tumbled on the stage in her towering Report Signature heels, surprising An who says she maneuvered easily in the shoes during dress rehearsal. "I freaked out when it happened, but think she just got caught up in the moment. She put so much energy into that amazing performance," says An.

For her second performance of Stevie Nick's "Rhiannon" Reinhart's flowing Tony Cohen dress was blown by a wind machine for a mystical effect reminiscent of the Fleetwood Mac singer's stage presence. "I actually didn't know about the wind machine, or that Haley was going to be singing that song when we saw that dress weeks ago, but at the time, we were thinking it was modern Stevie Nicks. The whole thing was karma." Reinhart's stunning Live! On Sunset sterling earrings featured crystals and teal gemstones, a choice An made for drama and "a pop of color against her skin."

Reinhart's third look, for a husky-voiced interpretation of Alanis Morrisette's "You Oughta Know", was a testament to the power of budget dressing. A royal blue Bebe camisole topped skintight black Old Navy jeans and dramatic Live! On Sunset shoulder-skimming earrings. "I love that they are jeans her fans can afford," says An. "The look is simple, but that goes a long way for Haley."

For more "American Idol" fashion scoop, read about the provocative shoes Lady Gaga wore for her visit last week.