She shopped at Christian Dior, Nina Ricci, Valentino, Pucci, Emanuel Ungaro and Pierre Cardin. She spent as much as $1.5 million a year on fashion in some years, her company estimates. But couturiers’ doors didn’t open easily for Eunice Johnson, because for a long time she was a rarity: an African-American fashion client.

Mrs. Johnson, who died in 2010, ran the Ebony Fashion Fair, a runway show that traveled around the U.S. from 1958 to 2009, displaying high fashion for an African-American audience. The wife of publishing mogul John Johnson, founder of EBONY magazine, she bought some 7,000 items of clothing and accessories over her lifetime, for the show and for her personal collection.

Now, curators at the Chicago History Museum are combing through her collection to create a March 2013 exhibition. Mrs. Johnson didn’t shy away from cutting-edge fashion, and the trove includes dramatic Pierre Cardin and Emilio Pucci designs from the 1960s and 1970s. There is also a well-known “Picasso” dress from Yves Saint Laurent, a gown designed by Alexander McQueen during his brief stint as Givenchy’s creative director and two Paco Rabanne hot-pant ensembles made of plastic discs.

“Anybody would be bowled over by what Mrs. Johnson was able to collect in her lifetime,” says Joy Bivins, the Chicago History Museum curator of the coming exhibition.

The collection also offers a window on a little-known moment in the civil-rights era when a rising class of African-Americans began to embrace a luxurious lifestyle that had been unavailable to them.

“Black society was never able to participate, and Mrs. Johnson made her own society,” says model Pat Cleveland, who got her start modeling for the Ebony Fashion Fair in 1965 as a teenager. “She was able to express what it was like to be able to be a luxurious woman.”

Mrs. Johnson traveled to ateliers in Paris, Rome and Florence during the buying seasons. Some designers, like Yves Saint Laurent (who is pictured with Mrs. Johnson above), welcomed her. Others took some convincing.

“We always had trouble getting in,” said Audrey Smaltz, a New York fashion-show coordinator who assisted with Mrs. Johnson’s buying trips and traveled with the fashion show in the 1970s. She says their team used the high-circulation EBONY magazine as a calling card or worked through a Parisian liaison.

Yves Saint Laurent was Mrs. Johnson’s favorite designer, says Linda Johnson Rice, Mrs. Johnson’s daughter and current chairman of Johnson Publishing Co., publisher of EBONY. “She would run backstage to greet him,” Mrs. Rice recalls, and he included her in events such as his 40th birthday party.

But at the Rome atelier of Princess Irene Galitzine, who popularized glitzy evening pants for women in the 1960s, Ms. Smaltz sat for an hour trying to get in to see the collection. Luckily, Vogue editor Alexander Liberman stopped in for an appointment, and his introduction helped open the doors, says Ms. Smaltz. (Both the princess and Mr. Liberman are now deceased.) “Can you imagine? They didn’t want to take our money,” says Ms. Smaltz, who traveled in style with Mrs. Johnson, sitting in first class on airplanes and staying at the Plaza Athenée hotel in Paris and the Excelsior in Rome.

Mid-century couture shows were exclusive affairs. Many clients knew each other. Some traveled together each season to order their wardrobes. “Let me tell you, she was alone doing this,” says Ms. Rice of her mother. “Flying to Europe sounds very glamorous, [but] here you are, you’re a black woman. There’s no one like you—no one even on the runway like you.”

She adds, “I think it was very lonely and it was tough. But she derived so much pleasure, because she loved the clothes and she loved the fact that she was going to bring them back for people to see them.”

Mrs. Johnson bargained ruthlessly with design houses’ vendeuses, or saleswomen, pulling out her checkbook to begin negotiations. “She would start to write the check, and she would stop and say, ‘You know, I really don’t think I like that price,'” says Ms. Rice, “and she would fold the check in half, [and] turn to me and say, ‘Linda, let’s go.'”

“The vendeuse, all she could see was this five-figure check walking out the door.” Mrs. Johnson, funded by her husband and their company, started out without a formal budget. From the 1970s through the 1990s, her spending averaged $1 million a year, Johnson Publishing says.

Mrs. Johnson’s buying missions resulted in an extensive personal haute couture collection, but a prime focus of her travels was clothes for the Ebony Fashion Fair. She also collected looks from African-American designers such as Patrick Kelly. The Johnsons “were trying to showcase the success and aspirations of African Americans and show really positive images of blackness to Black people,” says Ms. Bivins.

The Ebony Fashion Fair toured for up to six months annually, holding shows that raised funds for the United Negro College Fund and other causes. The show launched a generation of black fashion and Hollywood stars. “That was a turning point of my life,” says Richard Roundtree, an actor best known as the supercop Shaft from the 1970s cult films. Mr. Roundtree had been working as a catalog model when Mrs. Johnson hired him for her tour in 1967.

It was during an Ebony Fashion Fair party where he had a conversation with comedian Bill Cosby that encouraged him to study acting in New York, where he landed the Shaft role. Mr. Roundtree says the fashions he modeled fueled a sense that elegance was attainable. “This was Black people on stage with these incredible clothes,” he says. “They could totally relate to it because it was on bBack people.”

Traveling with the Ebony Fashion Fair was far from glamorous. Carole Brantley Pines, a 19-year-old model with the first show in 1958, says she was one of two light-skinned models who were sent in to get food at restaurants that declined to serve Blacks. In some Southern towns during the very early years, Mrs. Johnson’s husband arranged for food to be delivered to the bus “so we didn’t have to go to any back doors,” says Ms. Brantley Pines, who modeled under her maiden name, Carole Preston.

In the still-segregated South, they weren’t allowed to stay in hotels, so local groups would put up the models in their homes. “Beautiful homes. Black people were living very well, but we were still segregated,” she says.

During the Fashion Fair’s 1965-66 season, the Ku Klux Klan rallied outside a hotel in Little Rock, Ark., where the models were staying, Ms. Cleveland recalls. “We were scared to death—we were just trying to eat dinner,” she says.

“We were dressed in the best clothes,” Ms. Cleveland adds, describing the dozen or so models with a busload of traveling couture. In the South, “they understood that change was coming down the road.”

Eventually, some European designers turned to Mrs. Johnson for help as they courted a new African-American market. Mr. Pucci asked her to help him find Black models in the 1960s, Ms. Rice says. (Laudomia Pucci, the daughter of the late Mr. Pucci, says her father was a pioneer in working with Black models, and she remembers meeting Mrs. Johnson.)

The Ebony Fashion Fair was discontinued in 2009 when Mrs. Johnson, who died the following year at age 93, became too frail to oversee it. Ms. Rice and Johnson Publishing CEO Desirée Rogers, the former White House social secretary, plan to bring it back next year when the museum exhibit opens.

Virginia Heaven, a fashion historian who was consulted about the choices for the exhibition, says she was “stunned” when she first saw the collection Mrs. Johnson had amassed. “There were pieces that were iconic from Yves Saint Laurent, iconic from Lacroix,” she explains. Whittling down the choices has been difficult, she says. “We could have put together 10 exhibitions out of this material, and all would have been equally good.”