(CNN) Two weeks after closing Woodstock with his reinvention of "The Star Spangled Banner," Jimi Hendrix decided to offer a free concert for a group he called "my people."

He held a concert for an African-American audience in Harlem, a place he once called home. Hendrix's homecoming, though, was almost ruined as soon as he stepped onstage. Someone threw a bottle at him that shattered against a speaker; eggs splattered on the stage. Hendrix gamely played on while much of the crowd melted away.

"They didn't like him," says Charles R. Cross, who recounts the episode in his biography of Hendrix, "Room Full of Mirrors." "He was jeered. People heckled him."

A new film focusing on a more triumphant period in Hendrix's life is rekindling interest in the guitar icon. "Jimi: All Is by My Side" shows how Hendrix left New York for London to become a star. Yet no film has explored another twist in Hendrix's journey: How black and white audiences misunderstood the importance of Hendrix's race, both to the man and to his music.

Hendrix traveled to Harlem because he was trying to connect with blacks who had dismissed him as a musical Uncle Tom: a black man playing white man's music. Music critics and biographers say Hendrix also was frustrated by legions of white fans who only saw him as a racial stereotype -- a hypersexual black man who was high all the time -- instead of a serious musician.

There are signs today that more fans are starting to appreciate how Hendrix's race shaped his life and sound. Yet he's still seen by many as a musical genius who just happened to be black instead of a man whose genius was inseparable from his race, says Jeremy Wells, author of "Blackness Scuzed: Jimi Hendrix's Invisible Legacy in Heavy Metal."

Wells first noticed this pattern when he examined how white heavy metal musicians and fans described Hendrix. They rarely mentioned his race, or even said that his music transcended race. Wells said he found that odd given Hendrix's sound was steeped in the blues tradition of black guitarists such as B.B. King and Muddy Waters.

"Nobody would say that race doesn't matter for Muddy Waters," says Wells, an English professor at Indiana University Southeast. "But there's a whole industry devoted to saying it doesn't matter for Hendrix."

Race mattered more to Hendrix than most people realize, critics and biographers say: He was hurt by black radio's refusal to play his music; he experienced stinging racism during his time as an R&B sideman and star; and some of his most famous songs were profoundly shaped by his experiences as a black man in America.

Are they reading too much race into Hendrix's music? Here are three reasons why they say Hendrix's race mattered.

He took black music to Mars

Hendrix was post-racial before the term was even invented. Check out the photos from his four years as a star, and he seemed to live in a virtually all-white world. His two bandmates in the Jimi Hendrix Experience were white, his audience was virtually all-white, and most of his girlfriends were white. Hendrix even talked and dressed like a hippie, with his spacey verbal references, crushed velvet pants and bandannas.

Now close your eyes and listen to the growling guitar and wolf howls that Hendrix unleashes on songs like "Voodoo Child (Slight Return)," "Red House" and "Machine Gun." YouTube is filled with Hendrix's songs. He sounds like a black guitarist who one music critic said took "the blues out of the Mississippi Delta and sent it to Mars."

What Hendrix described as his "funky freaky" sound is drenched in blues. Hendrix spent his formative years listening to black blues guitarists such as T-Bone Walker and Curtis Mayfield. He honed his chops playing back-up to R&B artists such as Little Richard and The Isley Brothers on the "Chitlin' Circuit," a string of clubs in the segregated South that hosted black performers.

"He was widely understood to be the best R&B player of his time on the Chitlin' Circuit," says Greg Tate, a musician and a journalist who has written about Hendrix.

Hendrix expanded the range of the electric guitar when he became a star. He coaxed sounds from the instrument that no one had thought possible: "jet engines, oceans, exploding suns, and planets, wounded wildebeests, weeping seagulls," Tate wrote in an essay, "The 12 Best Jimi Hendrix solos."

"The electric guitar is an instrument whose history can be divided up into two eras: before and after Jimi Hendrix," Tate wrote.

Yet no matter how far out Hendrix's guitar sounded, the foundation of his music was always black music, musicians and critics say.

Eric Gales, a guitarist featured in Experience Hendrix , an all-star band touring the country playing Hendrix's music, says even on Hendrix's ballads, the blues seep through.

Listen to "Little Wing," one of Hendrix's best-known ballads, he says. It's filled with little guitar flourishes and a guitar tone that pay homage to Mayfield.

"Hendrix was not playing white man's music," says Gales, whose new album, "Good for Sumthin,' '' was released this month. "He took what was old traditional blues and R&B and amped it up. When white people started doing it, it was labeled their thing."

Hendrix's racial identity even suffused a song that at first glance had nothing to do with the blues.

His classic take on "The Star Spangled Banner" at Woodstock was noted for its sonic impact: Hendrix summoned the sounds of falling rockets and bursting bombs from his guitar. Yet others heard something more, a black man's protest. Hendrix played the song at the height of the Vietnam War, where black soldiers were dying in high numbers. He reportedly refused the pleading of his white business manager to forgo performing the anthem for fear of provoking a riot.

Hendrix's interpretation of the national anthem was a protest on par with King's "Letter from Birmingham Jail," says Wells, the English professor. Hendrix took a founding American document and reminded Americans how far they had strayed from their values.

"It was like Hendrix was saying, 'This is my country. This is my national anthem,' " Wells says. " 'Now look at what I'm going to do with it.' "

Hendrix was criticized for being unpatriotic after playing the anthem. When he went on "The Dick Cavett Show" after Woodstock , he told the talk show host he thought his version was "beautiful."

"I'm an American, too," he told Cavett.

He was racially profiled

It might seem odd to suggest that Hendrix's race was invisible to white fans; his skin color was one of his selling points when he burst onto the American scene in 1967 with his performance at the Monterey Pop Festival in California.

Hendrix may have been the first black sex symbol American whites unabashedly embraced. At a time when a black man could be killed for being with a white woman, Hendrix was surrounded by white groupies, flicking his tongue and grinding his guitar before thousands of cheering white girls.

These adoring fans certainly noticed Hendrix's race, but what they saw was actually a stereotype of the hypersexual black man that Hendrix played up for fame. The press of his day extended the stereotype further. Rolling Stone called him a "Psychedelic Superspade" while another magazine called him the "Wild Man of Borneo."

Few of these white fans knew, though, how much Hendrix's life had been marred by racism.

Hendrix left his hometown of Seattle because of racism, says Cross, his biographer. He grew up in a world of abject poverty and family turmoil that was typical of black families at that time. When he was a teenager, he was arrested on dubious charges of driving in stolen cars and given the choice of being jailed or enlisting in the Army, Cross says. He enlisted and became a paratrooper.

"What happened to Jimi would have never happened to a white male in that era," Cross says. "Jimi was run out of Seattle for being black."

Hendrix continued to experience racism as a musician. When he toured the Chitlin' Circuit, he couldn't go to the bathroom at gas stations in the South because they closed their doors to blacks. Even after he became a rock star, he was still racially profiled. Cross tells stories of Hendrix being mistaken for a bellhop in a swanky New York hotel, and of New York cabbies refusing to pick him up.

Even the rapturous reception Hendrix received when he traveled to London in 1966 for his first big break was tinged with racism. Various biographies of Hendrix noted that many of the white musicians he encountered had little exposure to black people and had difficulty accepting Hendrix as a superior musician. Some of their resistance to him was rooted in ego as well as race.

One infamous story tells how Hendrix had to kill God before he was accepted in London.

The Almighty was, in 1966, incarnate in Eric Clapton, the guitarist for Cream. He was considered so good that one graffiti artist in London declared, "Clapton is God." When Hendrix arrived in the British capital, he shocked onlookers by asking Clapton if he could join him onstage. Clapton consented and Hendrix launched into a blistering version of "Killing Floor," an up-tempo blues classic.

Clapton couldn't keep up and afterward stormed off the stage, humiliated.

"You didn't tell me he was this f***ing good," Clapton told Chas Chandler, Hendrix's manager.

After Hendrix died, some white fans still had trouble accepting Hendrix's race, says Wells, the music critic. Wells noticed that heavy metal artists hardly ever mentioned Hendrix's race as they raved about his guitar. They could hear his genius but they couldn't see his heritage.

That kind of adoration would not have pleased Hendrix, Wells says."He didn't want to be known as just a black musician," Wells says, "but he didn't want to be not known as a black musician."

He wanted blacks to celebrate his music

Before he held his ill-fated Harlem concert, Hendrix told a New York Times reporter why he returned to his old neighborhood.

"Sometimes when I come up here, people say, 'He plays white rock for white people,' " Hendrix said. " 'What's he doing up here?' Well, I want to show them that music is universal -- that there is no white rock or black rock."

Hendrix's quest for acceptance among his own people was a lifelong journey. He first tried to make it among black clubs on the Chitlin' Circuit, but his virtuoso guitar playing didn't fit the black popular music taste of the time.

"There was no place for Hendrix," Tate, the journalist, says. Black music then "was based around the style of singing, harmony and production of Motown."

Hendrix even stopped by black radio stations to encourage them to play his music to no avail, says Cross, author of "Room Full of Mirrors."

"It was very upsetting to him that he was not accepted in African-American radio stations," Cross says.

Hendrix didn't want to be confined by racial categories, but musical audiences were segregated like the rest of America, Cross says.

"Because Jimi played to white fans in an era of Black Power and separatism, they felt that he had betrayed his own race by having a white band and playing to an audience that was primarily white," Cross says.

Hendrix aggressively reached out to black audiences during the last two years of his life. He grew an Afro, wrote protest-themed songs and replaced his white bandmates with two black friends to form the Band of Gypsies. The group released a live album featuring Hendrix's classic, "Machine Gun."

The "Band of Gypsies" album gave hints of a new musical direction for Hendrix. He had befriended jazz musicians like Miles Davis who encouraged him to stretch. (The two had discussed making a recording together.) Hendrix was experimenting with larger bands, adding percussion and recording songs that sounded like a cross between jazz fusion and funk music. He told friends he was tired of the sexual showmanship and playing the Psychedelic Superspade.

Still, it would be a mistake to assume that Hendrix was on the verge of becoming a black militant. Hendrix's racial identity, some say, was like his music: ahead of its time.

There's one class picture of a young Hendrix that might explain why. The elementary school portrait is featured in David Henderson's biography, "Scuse Me While I Kiss the Sky." In it, a smiling, crew-cut Hendrix is surrounded by kids of all races: Japanese, Filipino, Native American, white. Hendrix was raised in a multicultural world -- he even had Native American blood.

Hendrix's high school was one of the most integrated schools in America in the 1950s, says Cross, his biographer.

"There was no school more diverse in America than Garfield High," Cross says. "He grew up in a world where race was not thought of as a barrier to music. It was not thought of as a barrier to friendship."

Today at least some of the barriers to seeing Hendrix's blackness are starting to come down, some say.

Hendrix has been sampled by hip-hop artists such as Public Enemy, A Tribe Called Quest and Frank Ocean. Groups like the Black Rock Coalition talk openly about Hendrix's influences. Rock, punk and metal are no longer seen as "white man's music."

"It's shifting," Cross says of black perceptions about Hendrix. "I get letters every day from young African-American men and women who say, 'Thank you for writing this book.'" Hendrix is even being included among the pantheon of black musical heroes. Previously, books and documentaries on great black musicians would mention people like James Brown, John Coltrane and Michael Jackson -- but not Hendrix.

That could be changing. Lamont Robinson created the "Official R&B Music Hall of Fame Museum" three years ago to honor black musical greats such as Whitney Houston, Marvin Gaye and others. He's in talks with four cities to find a permanent home for the museum by 2016.

Robinson says the museum has already decided on its 2015 inductees, and Hendrix is one of them. Blacks rejected him earlier, he says, but now more are starting to call him one of their own.

"If you had to build a Mount Rushmore to black music, you have to put his face on it," Robinson says. "It would have to go up there with Michael Jackson, Aretha Franklin -- he's right there."

Too bad Hendrix didn't live to see that day.

He died in London in 1970 after accidentally mixing too many sleeping pills with alcohol one night. He choked on his own vomit in his sleep. He was 27.

Hendrix had just built his own recording studio in New York and had spoken of taking time off to learn how to read music and play other instruments. He had changed so much from the shy unknown guitarist with acne who had come to Britain four years earlier.

In "Room Full of Mirrors," Cross recalls one of those magical moments in London when no one really knew Hendrix but turned out to see him because they sensed he was special.

Hendrix was playing at a London club and much of rock's elite -- the Beatles, Clapton, Pete Townshend, Jimmy Page and Jeff Beck -- walked in and sat on the front row to listen to this guitarist from Seattle.

During a break in the show, Brian Jones, one of the Rolling Stones' original leaders, ran into another musician returning to the stage to hear more of Hendrix.

"It's all wet down front," Jones warned the musician.

The musician looked puzzled so Jones explained.

"It's wet from all the guitar players crying."

Forty years after his death, it's still tempting to shed a tear listening to Hendrix -- not just because of what we hear, but for all the sounds we will never hear because he died so young.