“I haven’t heard applause like that for one of Zac’s shows in a long time,” said Bethann Hardison, a former model and agent, and an industry gadfly for diversity. “Zac set the tone for the rest of the week.”  At Mr. Posen’s show and in those of a telling handful of others this week, fashion, so it seemed, had performed an abrupt about-face.  Well before the Oscars stirred a diversity debate, Seventh Avenue had been the target of stinging criticism for the sin of omission, routinely parading mostly white models on its runways.  In this latest round of shows, which ended on Thursday, many designers appeared to have taken a hard look at the highly charged issue of casting, stepping up their efforts to hire racial and ethnic minorities and sounding a chord for inclusiveness.  That note resonated throughout the week. Multiracial runways may have been expected in willfully subversive collections like Puma x Fenty by Rihanna, Hood by Air, Telfar and Gypsy Sport, their producers scouring Instagram, Twitter and Facebook for models of varying ethnicities. Yet elsewhere it took spectators by surprise. Shows like those of Rosie Assoulin, Sophie Theallet and Tory Burch offered a bracing cocktail of skin tones.  There is no official tally of African-Americans populating the catwalks this week, but show-by-show estimates range in number from four or five at Anna Sui to 25 at Zac Posen and Xuly.Bët, whose designer, Lamine Kouyaté, had been vocal earlier this month about his intention to cast an all-black show.  But his mission proved daunting. One the eve of his show on Wednesday, Mr. Kouyaté had signed only 15 young women.  “Even that wasn’t easy,” his publicist Kelly Cutrone said. “There still aren’t that many black models at the agencies, and the ones that there are tend to be inexperienced. They haven’t had an opportunity to walk in many shows.”  Mr. Kouyaté was frustrated. “Since the 1970s, women of color have given input to the industry,” he said, referring to racially mixed runway extravaganzas of designers like Yves Saint Laurent. “Where are girls like that now?”  In Paris, Mr. Kouyaté noted, Olivier Rousteing of Balmain made a striking contribution to multiracial casting. Why not here? he asked.  “So much inspiration has been taken from black culture,” Mr. Kouyaté said, ascribing a rekindled fascination with African-American style and culture to the popularity of stars like Alicia Keys, Rihanna and Beyoncé. “They are the ones who have the power,” he said.  For all that, Ms. Hardison is seeing signs of progress. “Today there’s a market for these models,” she said from her front-row perch at Xuly.Bët. “That says something.”  “Some of those women are booked season after season, and that says something. And when the marketing people are not afraid to put girls of color in their campaigns, that says something, too.”  A heightened resolve to mingle skin tones on the runways was heralded by a spate of fashion advertisements in the spring glossies — dark-skinned models featured in previously white-dominated campaigns of Céline, Kate Spade, Chanel and Valentino, among others, the marketers apparently redoubling their efforts to be inclusive and to court a black consumer.  “Young people of color still are underrepresented on the runway,” said Kevin Amato, a casting guru for labels like Telfar, V-Files and Calvin Klein. “They’re the ones who want to wear the clothes, so we should be reflecting back to them versions of themselves on the runway.”  As Mr. Kouyaté insisted on doing at Xuly.Bët, bringing out, to the muted strains of a cello, a parade of restitched and recycled athletic jerseys, parkas, vibrantly colorful catsuits and faux furs to an audience that was, in roughly equal parts, white and black. Spectators leaned forward in their seats to gather an eyeful of the searingly bright street-inspired clothes.  Ms. Hardison was ebullient. Black models have indeed made advances since she began agitating for racial inclusiveness in a town hall gathering of industry leaders nearly a decade ago. She is watchful, just the same.  “Racism lays so dormantly, but it’s there,” Ms. Hardison said. “That’s why you have to keep after it, poking away.”  A version of this article appears in print on February 19, 2016, on page A23 of the New York edition with the headline: Widening the Runways. Order Reprints| Today's Paper|Subscribe
A handful of key shows, including Zac Posen and Xüly.Bet, put a more diverse fashion industry on display.