In a 1966 portrait currently on display at an art gallery in Manhattan, a dimpled young Indian woman sits on a deck chair, looking amused. Her mauve bandhani sari, its pallu wrapped snugly around her hips, accentuates her figure. The white of her petticoat is visible under layers of chiffon (too diaphanous to be polyester, not crumpled or starched enough to be cotton). Her blouse, also white, is sleeveless. Bollywood heroines started wearing sleeveless blouses in the 1960s, so she must have been quite fashionable.

She looks a little like Sharmila Tagore.

Her thick braid falls down her right shoulder and dangles below the seat. She poses with the long fingers of her right hand resting on her cheek, her chin a few inches above her palm. Her large brown eyes are lined with kohl, her gaze is confident. She stands out in Alice Neel, Uptown, an exhibition of selected portraits by the American artist Alice Neel at the David Zwirner gallery in Chelsea.

Neel painted these portraits during the five decades she lived in New York City’s Spanish Harlem and the Upper West Side, until her death in 1984. Most of them focus on African Americans and Latinos whom she encountered in her neighbourhoods and in the art world. The others are of people of colour too: Cyrus, the Gentle Iranian (1979); Abdul Rahman (1964), a Black Muslim; Ron Kajiwara (1971), the Japanese-American designer.

There is no information, however, about the only South Asian face here – just the title, Woman (1966).

Woman, 1966. Oil on canvas 46 x 31 inches Private Collection, Miami. © The Estate of Alice Neel. Courtesy David Zwirner, New York/London and Victoria Miro, London

She also remains conspicuous by her absence in the art historian Pamela Allara’s Pictures of People: Alice Neel’s American Portrait Gallery, which chronicles Neel’s life and work. Allara writes that Neel “revived and redirected the dying genre of ameliorative portraiture by merging objectivity with subjectivity, realism with expressionism”. Neel described herself as a “collector of souls,” Allara writes, adding that she was categorised as “a sort of artist-sociologist”.

Neel painted the mysterious woman a year after the 1965 Immigration and Nationality Act profoundly changed the American immigration policy, removing longstanding quotas on newcomers from India (among other places). Indians called it the “brain drain”, as the highly educated – particularly doctors – left for the American dream.

Was the woman in the portrait a young doctor then?

She wears gold jewellery – balis, a bangle, and a ring on her middle finger. A red bindi dots her forehead. A pinkish shadow on her hairline seems like the remnant of sindoor. She evokes a picture of Ashima Ganguli, the Bengali housewife in Jhumpa Lahiri’s The Namesake, set in the American North East during the same time period.

Neel had moved to a “more middle-class neighborhood” near Columbia University when she painted this young woman. Was she then a student at Columbia? Or a professor?

Hilton Als, a theater critic at The New Yorker, who curated the Alice Neel exhibition in Chelsea, writes, “In the years since her death, viewers young and old have experienced the kind of thrill I feel, still, whenever I look at Neel’s work, which, like all great art, reveals itself all at once while remaining mysterious.”

The identity of this sitter of Neel’s portrait does seem a great mystery. Even the internet offers no clues.

Ujjaini Bhattacharya, just before she left for the US.

The answer to the mystery finally arrived in an email from a research archivist at the David Zwirner gallery: “The sitter in the portrait is known to be the daughter of the Indian social-realist novelist Bhabani Bhattacharya (1906-1988), who had been invited to New York at the time by his American editor Millen Brand of Crown Publishers. At the time of this sitting, Bhattacharya’s daughter was enrolled as a student at Columbia University.”

Bhattacharya was a pioneering Indian writer who wrote in English. He was a contemporary of RK Narayan, Mulk Raj Anand and Raja Rao. His books were translated into several European and Indian languages. The New York Times’ literary critic Charles Poore, in a 1952 review of Music for Mohini, wrote about Bhattacharya’s protagonist Mohini: “We’ll all be lucky if we meet a more appealing heroine this year.”

It took five hours to locate his family. Their names are not in any academic paper, news clipping or obituaries about Bhattacharya, who spent the last two decades of his life in the US. His two daughters and a son are mentioned in a small 1988 funeral notice in the St Louis Post-Dispatch, a local Missouri newspaper: “Surviving are his wife, Salila Bhattacharya; a son, Dr Arjun Bhattacharya of Ladue; two daughters, Ujjaini Khanderia of Ann Arbor, Michigan, and Indrani Mukerji of Calcutta, India; and six grandchildren.”

Ujjaini Bhattacharya in 1967.

Ujjaini Khanderia of Ann Arbor, Michigan, avoids all calls from phone numbers she doesn’t recognise. She is particularly bothered by a caller who leaves a morbid message: pick up the phone or you will die.

She ignores the first message left on her voice mail asking for an interview, but answers the phone in the middle of the second.

Khanderia, now in her seventies, remembers when the portrait was made, but the details are hazy. She remembers the artist, but not quite. “She said would you like me to… I didn’t even know who she was, she made a portrait of me.” Khanderia speaks in fragments, then stops mid-sentence, gathers her thoughts and asks: “So tell me a little bit more. This is some famous gallery? What’s her name again?”

Fifty one years ago, Ujjaini Bhattacharya came to America on a scholarship to attend the University of Michigan. (She never went to Columbia, the gallery had the information wrong.) Before starting graduate school, she spent a week in New York City, where she lived with the family of her father’s friend and publisher Millen Brand.

“I was terribly homesick and wanted to go back to India the same day that I landed in New York,” she said. “I was NOT good company given my depressed and sad state of mind.” Brand took her sightseeing, and they stopped by at his friend Alice Neel’s studio apartment. Khanderia says she agreed to sit for the portrait. “Since I was lonely and homesick, I thought this was a good opportunity to be left alone without having to act friendly.”

When she met her now husband Sharad Khanderia in college, she remembers telling him about the “lady who drew a portrait of me. And that’s all. That was the end of the conversation.”

It never came up again, she said. She didn’t even think about it.

“I just thought she was a local artist,” she said. “I thought she was just practicing something.” She remembers Neel to be friendly and unassuming, engrossed in painting more than talking. She sat for Neel for about seven hours and was pleased by the finished portrait, “But my thoughts were elsewhere – I was more concerned about how I would survive in Ann Arbor where I knew nobody and had no help.”

She wondered whether her portrait can be shown in public without her permission. She said she never heard from Neel again. She tried to remember if Neel sent her a picture of the painting.

It was so long ago. It takes her a few minutes to get her bearings.

“Oh, so you’re going to be writing about the portrait,” she said, with a nervous laugh. “Ah, I thought you were writing something about my father. My goodness! That’s unbelievable! I could never imagine what you’re saying!”

The day she reached the US, Ujjaini Bhattacharya wanted to return to Nagpur.

In 1966, New York was a blur, in an America where Indians were not yet a “model minority”. They lived in the margins of American society, straddling the line that kept people of colour firmly outside. It was overwhelming for a 21-year-old from Nagpur. “I was too homesick to think about anything but home.” As a young student in Michigan, she said, “I was terribly afraid, I was totally unprepared. It was very scary. It was very, very difficult for me.”

It took her years to adjust to the country, the culture, the clothes. “I used to wear saris when I came to the US,” she said. “In Nagpur, we didn’t wear Western dresses, we wore saris more comfortably.” (She bought that mauve bandhani in Nagpur.)

She lost her way on the first day of college and was almost in tears when “a young student from India who saw my plight, offered to show me my way around campus”. Soon after Ujjaini Bhattacharya married Sharad Khanderia in America. They both eventually taught at the university’s College of Pharmacy. They had two children. This year, they will celebrate their 50th wedding anniversary. They still live in Ann Arbor.

Indians have been in the news in America the last few weeks, and America has been in the news internationally, the last few months. In the midst of vicious attacks and vitriol, Neel’s portrait gently celebrates Ujjaini Khanderia’s – and that of other people of colour – contribution and belonging to America.

Cyrus, the gentle Iranian, 1979. Oil on canvas 39 7/8 x 30 1/8 inches © The Estate of Alice Neel. Courtesy: David Zwirner, New York/London and Victoria Miro, London

Ron Kajiwara, 1971. Oil on canvas 67 7/8 x 35 1/8 inches © The Estate of Alice Neel. Courtesy: David Zwirner, New York/London and Victoria Miro, London

Alice Neel, Uptown was on display at the David Zwirner gallery, New York City, till April 22. It will be on show at the Victoria Miro Gallery, London, from May 18 to July 29.