When Laura Bell Bundy — the star of the hit Broadway musical “Legally Blonde” — saw the clunky, custom-made dance shoes she was expected to wear onstage, she rejected them outright. “Elle Woods would never wear hospital shoes,” Ms. Bundy said.

In response, Tony Award-winning costume designer Gregg Barnes came up with alternative footwear from Prada, Christian Louboutin, and Betsey Johnson, all of which Ms. Bundy has happily worn since “Legally Blonde” opened on Broadway in April. The delicate designer footwear forces her to balance on the balls of her feet throughout the show to avoid catching a stiletto heel in the tracks where the scenery slides into place. But it’s worth it. “It was a character choice, believe me,” Ms. Bundy said, while standing in her pink-walled dressing room at the Palace Theater. “I was willing to do whatever it took.”

Combining the magic of Broadway with believable character wardrobes was a challenge for Mr. Barnes in designing costumes for “Legally Blonde.” In the lighthearted musical, Elle abandons the pastels of her California sorority house for the houndstooth and khaki of Harvard Law School. Based on the film starring platinum-coiffed starlet Reese Witherspoon, the show has netted seven Tony nominations, including one for Mr. Barnes’s costumes.

With elaborate dance numbers and a song named “Omigod You Guys,” the show risked becoming a caricature of itself, Mr. Barnes said. He worked to sidestep that tendency with the show’s 275 costumes. “The story could be a very cartoonish experience — that’s what the audience expects,” Mr. Barnes, who won a Tony in 2006 for the fantastical, 1920s-era costumes in “The Drowsy Chaperone,” said. “Part of the challenge is finding the fine line between heightening it for the quality of storytelling a musical needs and keeping it honest so they look like real people.”

In preparation for the show, Mr. Barnes and his assistants roamed the streets of Boston, New York, and Los Angeles’s Rodeo Drive, taking snapshots as they went. They pored over celebrity gossip magazines and browsed couture collections. All the costumes in the show are based on clothing Mr. Barnes saw along the way, including Elle’s first costume, a simple white minidress inspired by a snapshot of a blond woman walking down Fifth Avenue.

Mr. Barnes then set about recreating the looks he’d admired. The show is unusual for its mixture of purchased and custom-built costumes, Mr. Barnes said. His team bought much of the scruffy, scholarly attire worn in the Harvard Law scenes, in contrast to the specially designed “Juicy-Couture-goes-to-the-sorority-house” — as Mr. Barnes refers to it — garb sported by Elle’s California girlfriends. But many of the show’s costume changes — including 16 for Ms. Bundy alone, way above the average 10 for a Broadway leading lady — are so quick that they require custom-made, layered garments that peel off with a single zipper down the back.

Actors are notoriously particular about their costumes, but Mr. Barnes listened to their suggestions. At the request of Christian Borle, who plays Emmett, Elle’s law-school love interest, Mr. Barnes procured a T-shirt bearing the words “New Mission High,” a school in the “Roxbury slums” where Emmett grew up. For Paulette, the downtrodden hairdresser, Mr. Barnes’s team snapped a photo of her beloved bulldog, Rufus, and embroidered the image on a shirt. “We tried as hard as we could to make a detailed backstory for everything in the show,” Mr. Barnes said.

In “Legally Blonde,” clothing is crucial in illustrating Elle’s struggle to adapt her party-girl persona to her professional ambitions. “Elle needed to start pink, then lose her signature color as she loses a part of who she was, and then regain it as she marches back to the trial,” the director and choreographer of “Legally Blonde,” Jerry Mitchell, said. “The old saying ‘don’t judge a book by is cover’ is a theme. That was what we wanted to do — to be able to judge instantly, before the characters spoke. That way, as the characters grew, so could their appearance.”

In part because of the show’s thematic reliance on labels, the show inked an unusually high number of promotional tie-ins. Tiffany & Co. designed a locket for Elle and her pet Chihuahua, Bruiser. The hair product company Matrix stocked Paulette’s beauty salon. While many of the purses in the show are replicas, the cast also makes use — through a promotion — of four Lana Marks handbags, each of which retails for between $12,000 and $18,000. “The thing I love about placing a product like that, especially a luxury item that we couldn’t have afforded without that tie-in, is that the audience knows,” Mr. Barnes said. “It brings a whole history to the character, just by what they carry.”

The show also includes several “very flashy ” moments, Mr. Barnes said, such as Elle’s lightning-quick, onstage costume change in the first act. And dressing Chico and Chloe, the two canine stars of “Legally Blonde,” presented quite a challenge. Bruiser’s winter jacket, for example, had to be taken apart and stripped of the fiber filling to keep the dog cool and comfortable onstage, Mr. Barnes said. Ultimately, he found it easier to match Ms. Bundy’s clothes to Chico, instead of the other way around. Moreover, many of the human costumes had to be built with plastic-lined pockets for doggy treats, to prevent the greasy snacks from staining the clothes.

Mr. Barnes is no stranger to Tony Awards. Three years before his award for “The Drowsy Chaperone,” he was nominated for the costumes in “Flower Drum Song.” This Sunday evening when the Tony Awards are presented, he may well add another win to that impressive roster.