She wants to rescue another orphan - but only if it's the right colour. He's trying to save the world at ¡ê2m lobster and champagne parties. Are Brad and Angelina Hollywood saints ... or just bonkers?

A huge black four-wheel-drive Audi people carrier tears down the narrow streets of Prague, and without warning screeches to a shuddering halt. Slowly, a tinted rear window descends as an emaciated arm appears and points a bony finger, ET-like, in the direction of a bemused passing pedestrian.

Seconds later, the car roars off again before stopping at an exclusive school in the city. There the bird-like and brittle figure of Angelina Jolie emerges and, flanked by a contingent of suited bodyguards, delivers her five-year-old son Maddox to morning class.

These unscheduled stops on the school-run have become something of a regular occurrence in recent weeks since the actress, her lover Brad Pitt and their family set up home in the Czech capital while she works on her latest film.

Invariably the passers-by she points out to her son in this predominantly white city are black or Asian.

And the reason for this strange behaviour? Miss Jolie is keen, according to those close to her, to seek the boy's advice about the exact skin colour she should choose for the next addition to her "rainbow coalition" of adopted children.

Angelina has decided, she has told friends, that her fifth child will come from Africa. She already has Cambodian orphan Maddox, five, a two-year-old Ethiopian girl called Zahara, Shiloh, her natural baby daughter with Pitt, who celebrates her first birthday tomorrow, and the most recent arrival, three-year-old Pax Thien from Vietnam.

The beautiful Angelina is said to have chosen Pax - the boy she adopted in a blaze of publicity at the end of March - because of his uncanny likeness to her eldest son. Now, she has decreed, Zee - as Zahara is known to her famous parents - must have her own lookalike too, so she will not feel left out.

Welcome to racial profiling Hollywood-style. Not, it should be said, that such behaviour is the extent of the eccentricity of Tinseltown's hottest but increasingly bizarre couple.

Witness Pitt's performance hectoring guests this week at a ¡ê300-a-head charity party the pair threw during the Cannes Film Festival, to celebrate the premiere of A Mighty Heart, in which 31-year-old Angelina gives a bravura performance as Mariane Pearl, the wife of Wall Street Journal reporter Daniel Pearl, who was beheaded by Islamic extremists.

Pitt, whose slicked back hair and dinner suit on the red carpet lent him an uncanny resemblance to Robert Redford in The Great Gatsby, is said to have button-holed VIPs at the soiree, in a villa in the grounds of the luxurious Hotel Du Cap, to share his dark pronouncements about the state of the planet and the effects of global warming.

At the same time, Pitt, who has taken over four suites at the hotel for his family costing ¡ê9,000 a night, was playing up his globally conscious credentials in public, saying: "I look at my kids and know they will inherit this world. I want to do all I can to throw our weight in and make it a little better."

A noble intention, but somewhat at odds with his own carbon footprint, which, it has to be said, has reached gargantuan proportions of late.

Bored while his girlfriend films her latest movie Wanted, Pitt has had his eight-litre, 250mph Bugatti Veyron shipped over from California to Prague to give him something to do. (It is the sort of nine-miles-per-gallon, ¡ê700,000 boy-toy racing car that every self-respecting eco-warrior should own).

And when he has time to take a break from looking after the children, he is indulging his love of the air by having daily two-hour helicopter lessons (paid for by her generous film company) so he can add a chopper to the private plane he pilots.

As if that were not polluting enough, the couple, who travelled to France by private jet, are said to be in negotiation with an Italian firm to take delivery of a ¡ê100million super yacht.

The 280ft vessel, which comes complete with its own glass-fronted submarine that can be launched from its hull, has eight decks, seven lifts and can carry eight limousines, three helicopters and a seaplane. It comes fitted with his and hers "wellness centres", sauna and spa baths.

It will even dwarf the RM Elegant, the yacht moored this week off the Cap d'Antibes, which hosted the "party to end all parties". The shindig saw the couple join 200 guests who had paid up to ¡ê100,000 each, for a charity event hosted by Warner Brothers to help end genocide in the Darfur region of the Sudan (it also served to publicise Pitt's appearance in Ocean's 13).

On hand to entertain this oh-so-socially aware celebrity set, which included Matt Damon and Al Pacino, were circus acts and magicians, while they dined on lobster and beef with truffles, and sipped their way through 500 bottles of Krug and Cristal champagne.

No wonder then that back in Tinseltown the knives are out for the couple, known universally by their combined moniker Brangelina.

While La-La Land has been rife for months with rumours about the strained state of their relationship (they hardly silenced the snipers with a glum performance on the red carpet this week), Angelina has found that her Mother Teresa image has taken something of a dent.

She has come in for a torrent of abuse in America over claims she has been shamelessly using her children to get herself publicity. Her cause was not helped when it emerged that, while she has been telling anyone who will listen that she intends to take a year off to spend with her ever-increasing brood, she has lined up at least two more highly paid movie roles.

The couple have not been slow to put their children before the camera when the mood has suited them. Less than a week after their most recent adoption of Pax Thien, which means Peaceful Sky (it was chosen by the couple, who didn't like his original name, Pham Quang Sang), Angelina was posing on the cover of Hello! magazine with the three-year-old. In their defence, she did give the reported ¡ê1million she received for the pictures to charity.

Nonetheless the couple, who are said to have argued over Angelina's determination to go through with the adoption, were later accused of fast-tracking the previously strict legislation about foreigners taking children out of the country.

Meanwhile there are dark - and, it should be said, fanciful - rumours doing the rounds about her "close" friendship with up-and-coming 28-year-old British actor James McAvoy, with whom she stars in the thriller Wanted.

Earlier this month the Glasgow-born actor was forced to issue a denial over the tittle-tattle about him and his new leading lady.

At the same time, one Hollywood gossip website has christened Brad "America's Number One Desperate Househusband" over his transformation from sex god to nappychanging earth father (he has become the legal guardian of Maddox and Zahara).

Pitt, who was still married to his first wife, Friends star Jennifer Aniston, when he met the formidable Miss Jolie on the set of Mr And Mrs Smith in 2004, is said to carry out most of the child-rearing chores.

He is taking, on her insistence, cooking lessons because she maintains that their multi-cultural family must eat the indigenous foods of their homelands.

Indeed, while her career flourishes (the Tomb Raider actress has received rave notices for her role as French-born Mrs Pearl), Pitt has experienced his first potential cinematic flop.

This month he learnt that his "poetic" film about the life and death of outlaw Jesse James, in which he stars, will be released only in a small number of American art house cinemas.

Studio heads at Warner Brothers are said to have pulled funding after failing to persuade Pitt, 43, who has ¡ê20million of his money tied up in the project, to turn the slow-paced drama into an action-packed blockbuster.

Miss Jolie has her own share of troubles. This week, as she put herself on show in France, she appeared painfully thin and drawn. According to some within her entourage she has "barely eaten" since the death from cancer of her mother Marcheline Bertrand in January.

This week a clearly fragile Angelina broke down in tears on U.S. network television as she admitted: "It's been a heavy year. I lost my mum too young."

A further cause for concern is an alleged ¡ê50million threat to kidnap one of their children. While in Europe, the couple have hired a team of highly trained and mainly British security men to protect them.

Not that it has stopped them keeping an unusually high public profile as they attempt to play down those rumours about the "dire state" of their relationship.

Earlier this month, and just as reports in the U.S. claimed they were undergoing counselling, their staff tipped off photographers that they would be enjoying a "romantic dinner" at a tiny Prague restaurant.

Now is not a good time for unwanted gossip, particularly as the couple do not want to draw attention away from Miss Jolie's role in A Mighty Heart, which Pitt produced through his company Plan B and which is already being tipped to win her a second Oscar.

So it is all the more embarrassing for the couple that Miss Jolie should go blurting out to one interviewer who questioned her about their relationship: "So many parents today do separate and they still have a commitment to the children."

And heart-throb Brad is said to have agreed to re-shoot kissing scenes with his glamorous co-star Megan Brown during filming of his latest film, The Curious Case Of Benjamin Button, in a bid to tone them down and pacify Miss Jolie.

A source close to the couple told the Mail: "If they look unhappy it is because they are. Angelina has been very down over her mother, and Brad, for all his posturing about saving the world, is a big kid who loves nothing better than driving round in his latest toy.

"They have become so far removed from reality they have no clue how they appear to anyone outside their friends and coterie of celebrities."

No wonder, then, that Miss Jolie is taking her mind off things by choosing the skin tone of that next addition to the United Colours of Brangelina.