In Mr Lauren's sophisticated world women wear black ... and white

It's a truth that American designers are more commercially focused than their artsy European counterparts. But, at the moment, there is only one designer in New York who runs a genuine global fashion empire.

Ralph Lauren presented his spring/summer 2007 womenswear collection yesterday - the most expensive of the myriad lines that sustain his publicly listed company.

According to the Forbes 2005 rich list, Lauren is worth $2.8bn (£1.5bn). That doesn't stop him from taking his finalé bow, stopping to embrace guests Kevin Costner and Lauren Hutton, in hole-riddled cowboy jeans and chambray shirt.

There was nothing rough and ready about this show, held at a photographic studio in SoHo, though: taking a North African colonial theme, he sent out clothes for the kind of woman who travels with a retinue.

"A sophisticated woman with eclectic individual style and an exotic, independent spirit," purred the show notes, although eclectic turned out to mean that she not only wears black, but also white, and her independence certainly doesn't stretch to include carrying her own bags.

Ralph Lauren's woman wears crease-free white linen shirt dresses and a Panama hat during the day, and, at night, old-gold lamé 1920s dresses, inlaid with glittering Art-Deco embroideries.

And she most certainly doesn't get sweaty armpits - or slouch around in Havaiana flip-flops.

If that all sounds a little unreal, well, Ralph Lauren's stock in trade is a fantasy of old-world privilege. He was the designer chosen to costume the 1974 film version of The Great Gatsby, and whether his preppy world-view appeals to you or not, it's one that he executes to perfection.

Even a garment as simple as a clingy black silk slip dress, for its faultless fit, exuded sophistication. This show won't change the direction of fashion - Lauren mostly ignored the consensus for loose, airy dressing that has emerged for next spring - but it meets the requirements of women who want to look classy, rather then cool.

Zac Posen, a 25-year-old designer much hyped by the American press, could do with taking a few tips from Lauren. Posen, who showed late on Thursday night, has an unlikely financier in the rap impresario P Diddy, and he has plenty of celebrity supporters. But his handling of couture-grade fabrics and fiddly details - swags of beading at the shoulder of a jacket, or the liquid satin of a pale grey Jazz Age dress - lacked polish.