“The whole thing was completely against anything that I had ever witnessed, anything I had ever studied, anything I ever knew,” she said in a 2004 interview for the Criterion Collection.

Ms. Goldoni, who died July 22 at 86, became one of the workshop’s star students, participating in marathon improv sessions that laid the groundwork for Cassavetes’s directorial debut, “Shadows” (1959). The film, which starred Ms. Goldoni as a light-skinned Black woman seduced by a young White man (Anthony Ray), became a landmark of American independent filmmaking, admired for its unvarnished depiction of romance, family and interracial relationships.

“ ‘Shadows’ showed viewers the world Hollywood was missing,” wrote Steve Rose of the Guardian, in a 2010 feature on the best art-house films of all time. (“Shadows” came in at No. 19.) “It narrowed the gap between film and reality, and it planted the previously unthinkable idea of making your own movie into the heads of many a subsequent young auteur.”

Ms. Goldoni went on to appear in more than 60 movies and TV shows, working with acclaimed directors including Martin Scorsese (“Alice Doesn’t Live Here Anymore,” 1974), John Schlesinger (“The Day of the Locust,” 1975) and Philip Kaufman (“Invasion of the Body Snatchers,” 1978).

But she remained best known for her poignant, naturalistic performance as an aspiring painter in “Shadows,” in which she starred opposite Ben Carruthers (whom she married before the film was finished) and Hugh Hurd, who played her older brothers.

As Lelia — the film’s characters shared the same names as the actors — she delivered one of the movie’s most memorable lines, gazing into the distance while lying in bed after her first sexual encounter with Ray’s character, Tony: “I never thought it could be so awful.”

The line was scripted, although a title sequence at the end declared that the movie was “an improvisation.” Almost all of all the film was scripted, although the plot developed out of the improv sessions in Cassavetes’s workshop and the production itself had a makeshift, improvisatory feel: The movie was shot on the streets of New York with a handheld 16mm camera for only $40,000, or about $420,000 in today’s money.

“We were doing what is now called guerrilla filming,” Ms. Goldoni told the San Francisco Chronicle in 1991. “We had no street permits, so we’d take the camera out in a grocery cart, powered by a car battery. Policemen would come by and John would grease their palms. They’d go away and another couple of cops would come along.”

Cassavetes unveiled an initial version of the movie in 1958, then decided he needed to rework it and shoot additional scenes. The final version, released a year later, received mixed reviews — New York Times film critic Bosley Crowther called it “fitfully dynamic, endowed with a raw but vibrant strength” — but gained steam after it was honored at the Venice Film Festival. In 1993, it was inducted into the National Film Registry.

The film brought Ms. Goldoni a nomination for a BAFTA, the British equivalent of an Oscar, although it proved a mixed blessing for the actress. In a reverse form of the racial passing depicted in “Shadows,” she was a daughter of Italian immigrants, not a Black woman like the character she played on-screen. By her telling, she found herself largely shut out of Hollywood at a time when Black performers had limited opportunities in mainstream film and television; she had better luck in England, where she worked for a decade before returning to the United States.

“People were so convinced I was Black that I couldn’t get work,” she said in the Chronicle interview. “The English thought I was kinky and the Americans wouldn’t hire me with a 10-foot pole.

“Several years ago,” she added, “the head of casting at CBS told me he thought I was lying when I said I was Italian.”

Lelia Vita Rizzuto — she changed her last name to Goldoni around the time she started acting — was born in Manhattan on Oct. 1, 1936.

Her father, an actor, died when she was about 18 months old. Her mother, a seamstress, set out to rebuild her life and moved to Los Angeles with Ms. Goldoni, her only child. She remained haunted by her husband’s death; her grief, and relationship with Ms. Goldoni, inspired a play, “Who’s Looking After the Baby?,” which was staged in Sherman Oaks in 1994 by Ms. Goldoni and written by her third husband, Robert Rudelson.

Ms. Goldoni made her uncredited film debut in 1949, the year she turned 13, appearing in John Huston’s “We Were Strangers” and Joseph L. Mankiewicz’s “House of Strangers.” At the time she was more interested in dancing: She had started hoofing at age 5 and, as a teenager, she performed with choreographer Lester Horton’s racially integrated dance troupe, which also featured Alvin Ailey and Carmen de Lavallade.

Encouraged by Ailey, Ms. Goldoni later directed and produced a documentary about Horton, “Genius on the Wrong Coast” (1993). “He was such an incredible powerhouse,” she told the Los Angeles Times, “and no technique that I saw, and no choreography, ever grasped me in the way Horton’s work did.”

After Horton died of a heart attack in 1953, she lost interest in dance and then moved to New York, where she said she discovered that Cassavetes “had the same kind of charisma” as her dance mentor. She soon worked out an agreement with the director: in exchange for teaching the other workshop participants how to dance, she could attend acting classes free.

Ms. Goldoni later worked with Cassavetes on TV shows including “Johnny Staccato,” in which he starred as a piano-playing private detective, and “The Lloyd Bridges Show,” on an episode he directed. She continued to appear on TV for more than five decades, including on episodes of the British spy series “Danger Man,” with Patrick McGoohan, and the World War II miniseries “The Pacific,” on HBO.

While in Britain, she landed a small role in the crime comedy “The Italian Job” (1969), as the alluring widow who gives Michael Caine’s thief character the plans for a heist. She had married Rudelson, an actor and writer, the previous year, after her earlier marriages to Carruthers and William B. Hale ended in divorce. They soon moved back to Los Angeles, where she appeared in movies including “Bloodbrothers” (1978), as the mother of Richard Gere, and raised a son, Aaron Rudelson.

Ms. Goldoni died at a nursing home in Englewood, N.J., of complications from Alzheimer’s disease, according to her son. He survives her, as do two grandchildren. Her husband died in 1997.

Late in her career, Ms. Goldoni taught acting workshops and performed on the stage, collaborating with the New York theater troupe Hoi Polloi after seeing its 2011 stage adaptation of “Shadows.” The group’s 2013 program “Beckett Solos,” a trio of short plays by Samuel Beckett, starred Ms. Goldoni, then 77, in multiple roles, repeating mournful lines like “Close of a long day” as though her character was looking toward death.

“Stark and ambient, [the program] captures Beckett’s singular music of alienation,” wrote New York Times theater critic Andy Webster. “And Ms. Goldoni makes a fine instrument.”