By WENDY DONAHUE • Chicago Tribune

An interior design riddle: For every four-sided room, how many walls are there to consider?

Six, according to Dallas-based designer Elaine Williamson. And for many clients, the floor has become the most important one.

Allergies, animals and eco-consciousness continue to roll back the wall-to-wall carpet in favor of a hard surface. So the key mood-setter/style dictator becomes ... the rug.

It might be anything from an unobtrusive sisal to a penetrating Fornasetti gaze (roubinirugs.com). What it's less likely to be these days, in a new space anyway, is a classic Oriental.

"For the most part clients aren't even asking about them anymore," Williamson said. "There's a new breed of rugs out there, and it's very design-oriented, sophisticated and artful."

In the "Sex and the City 2" movie, the most eye-catching styles have moved from the stars to the sets. The red and pink blooms on the "Candy Flower" rug steal the spotlight in the otherwise mostly neutral living room of Carrie (Sarah Jessica Parker) and John (Chris Noth). The rug even has fashion credibility, created by designer brand Marni for the Rug Co. (therugcompany.info), one of a few that specialize in statement-making rugs, often in collaboration with fashion designers, artists and architects.

Still, it's an overstatement to say a rug should always be the masterpiece, or even square one, for a room, said Margaret Russell, editor-in-chief of Elle Decor.

The foundation

"The starting point should be something you love," she said. "If that's a rug, that's great, because it is the foundation, the base, of what everything goes on. A lot of people look at a rug as a focal point. Others look at it as the equivalent of a good paint job."

Rug layering has added another dimension. Sisal in summer can be topped with a heavier rug in winter. Or sisal can be embellished -- famously, in a rug belonging to George Stephanopoulos and his wife, Ali Wentworth.

"They have an aging family dog, and the dog had had a few accidents on it," Russell recounted from a story that made the cover of Elle Decor as well as the "Oprah" show.

Wentworth wanted a new rug; Stephan-opoulos didn't. So Wentworth bought fabric dye in lavender.

"She did this almost starburst pattern all over this creamy rug," to disguise the dog's crime scenes, Russell said. "George came home and said, 'I told you I didn't want to get a rug yet!'

"Sisal doesn't need to be boring," Russell said.

William Diamond, of New York-based Diamond Baratta Design, often centers his interiors on bold custom rugs. "We think that a rug is a great place to put your style because it sits on the floor," he said. "Even if it does have a lot of style, it doesn't smack you in the face. When you bring design up higher, in sofas, chairs, walls, it's hitting you in the face more."

That's why he also believes in keeping the furniture simpler, and having some coordination between it and the rug colors.

Just as at a dinner party, he said, "you can't have everything be the center of attention."