Trey Speegle's giant paint-by-number canvas spelling out the word YES at the back of Stella McCartney's runway summed up the mood of today's collection quite succinctly. These were uncomplicated, upbeat, and above all colorful clothes for women who prefer not to think too hard about getting dressed but still want to look young, sexy, and chic. It's a sentiment that McCartney, a mother of three young children and the head of a growing fashion empire, understands intimately—as do her loyal customers, including front-row pal Gwyneth Paltrow.

The actress, who sat sandwiched between Stella's dad, Sir Paul, and Charlotte Rampling, wore a McCartney blazer and skinny denim. Both made appearances on the runway, but these weren't the designer's signature elongated, borrowed-from-the-boys shapes. Instead, she took her tailoring in a more feminine direction. Jackets in silvery raw silk shantung came with a graceful ruffle down one lapel, or a sweet peplum, and were paired with wrapped-waist, relaxed silk pants. Denim turned up as a pinafore and as easy button-front A-line skirts, worn with a silk shirt or a lace cami and jacket. Wedge cork Linda sandals, inspired by McCartney's late mother, complemented the clothes' slightly retro seventies feel.

"Summer's not about aggression," the designer said backstage, and that thinking extended into evening, for which she proposed red, blue, and orange rose-print pleated dresses edged at the neckline and hem with swirls of ruffles. The collection won't necessarily situate her in Spring's big conversations about sheerness or lingerie (she did transparency and lace last season). Not that she minds. "I wanted to teach my customers not to be afraid of the simple stuff," she said. McCartney clearly isn't, and it's that kind of confidence that makes her clothes so winning.