Because of the hyperbolic hairstyle and self-tanner that had developed deeper than her own voice, Ms. de Lesseps was accused by fans on Twitter of being in blackface. She later appeared on “Watch What Happens Live,” Bravo’s late-night show, and denied that she had done anything wrong. Still, she apologized, saying, “I love Diana Ross. I totally respect Diana Ross. It was really kind of a tribute to her. It was Halloween!” She added that she applied no additional color to her skin, other than bronzer, and “would never dream of doing a blackface, ever.”

Only one “New York City” cast member, Carole Radziwill, acknowledged the transgression on the show before it was mostly forgotten about for the rest of the season.

But what if there had been an African-American woman on the cast? And, of course, the bigger question: Why has there never been a black woman on the cast of “New York City”? According to the most recent United States census, 24.3 percent of New York City’s population is black, 29.1 percent is Hispanic, and 42.8 percent is white. If less than half of the city is white, why is 100 percent of the cast of “The Real Housewives of New York City” white?

And are the people making the show concerned about this?

“Absolutely, it bothered me,” said Heather Thomson, who was a cast member from 2012 to 2015. “I advocated for more diversity while I was on ‘The Real Housewives of New York City,’ not only to showcase the reality of NYC, but also my own true circle of friends.”

Her professional and social circles were notably more diverse than some of her castmates. Before founding her shapewear company, Yummie, she was the founding design director of Sean Combs’s label Sean John and worked closely with Jennifer Lopez and Beyoncé to develop and introduce their clothing lines. If ever there were a white bridge to an elite crowd of affluent nonwhite women in Manhattan, Ms. Thomson was it.

Ms. Thomson said that after her first season on the show, she recommended several women of color to producers. The producers “were wide open to it,” she said, and they contacted the women she recommended, but ultimately “were not successful in finding the right individual to fill the void.”