SACHA WALCKHOFF, a Paris-based fashion and product designer, was astonished when the wildly floral wallpapers he introduced in lime green and fuchsia two years ago became big sellers. “Even me, I would think twice about using them,” he confided.

That says a lot. Mr. Walckhoff is creative director of Christian Lacroix, the French fashion house with a mile-wide streak of flamboyance. The colorful, pattern-mad brand, which six years ago began producing home décor, has always appealed to people with courage, but in the last two...