TWO black men pass a white woman on a shopping street in Beverly Hills. She reacts by clutching her handbag and stepping aside.

For one, the woman’s reaction smacks of racism. The other argues that they were just taking up too much room.

The explanation for this difference in perception is that one of the two is actually a white man in disguise. No prizes for guessing which.

Bruno Marcotulli and his family agreed to swap races for six weeks with Brian Sparks’s black family for a pioneering reality television show that premiered in the United States last night, called Black. White.

On the show, Mr Marcotulli accuses Mr Sparks of finding racism where it does not exist. “You see what you want to see,” he says. “And you don’t see what you don’t want to see,” Mr Sparks retorts.

The six-part series, dubbed “Trading Races” by critics, was produced by the documentary- maker R. J. Cutler, who produced The War Room about Bill Clinton’s 1992 presidential campaign, and the rapper Ice Cube.

Coming just days after the Oscar victory of Crash, it testifies to America’s abiding fascination with race.

Black. White. updates a tradition of racial impersonation dating back at least to John Howard Griffin’s 1959 classic Black Like Me, in which the white author travelled the Deep South with his skin dyed black.

The show employs Keith Vanderlaan, a Hollywood make-up artist, nominated for an Oscar for The Passion of the Christ, to transform the Marcotulli clan from liberal Santa Monica into blacks and the Sparks, from Atlanta, into whites.

The make-up, using prosthetics and hair pieces, takes five hours a day to put on and another hour to remove.

Mr Marcotulli, 47, a teacher, explains that he was born to Italian immigrant parents who taught him that ethnic minorities must pull themselves up by their bootstraps. But he quickly falls foul of his black peers when he starts practising a “black” walk and proclaims that he is looking forward to having someone insult him with the N-word.

His girlfriend, Carmen Wurgel, 48, a location scout whose parents were active in the civil rights movement, is the more overtly liberal of the two. But she cannot avoid putting a foot wrong either.

During a diction tutorial, she affectionately greets her black counterpart “Yo, bitch”, which goes down like a lead balloon. She causes further offence when she calls a visitor a “magnificent black creature”.

Mr Sparks corrects her: “The only creatures I know are the Thing, the Blob, Jason, Freddy — you know, creatures.”

Ms Wurgel’s college-going daughter, Rose Bloomfield, 18, admits that she was concerned about getting involved in what could be seen as a “minstrel” show. But she fares better.

Rose, in blackface, enrols in a Hollywood poetry slam class with other black teenagers. Asked to name their favourite poets, the others praise Prince, Michael Jackson and Mary J. Blige. Rose names the Irish rock band the Cranberries. But eventually she confesses that she is really white. “They were more civil than I thought they would be,” she says.

White mother and daughter learn about racism first-hand when they go, as blacks, looking for a job in the trendy shops of West Los Angeles and find that the managers are unavailable or the application forms out of stock.

The Sparks family get a more direct experience of prejudice when masquerading as whites — although their 17-year-old son, Nick, seems oblivious.

Made up as a white, Mr Sparks’s wife, Renee, has to suffer a white man in a focus group recounting how he was taught as a child to wash after shaking hands with a black person. Mr Sparks, 41, a building contractor, is shocked to have an assistant in a golf shop actually put a pair of shoes on his feet and lace them up.

“It’s never happened to me as a black in 40 years, but the first time I go and buy shoes as a white, I have it done,” he says.

Times Recommends

• Please help: maimed children of war want their lives back
• Cabal seizes diamond riches to buy power
• White House gatecrashers got to the president