Where does excess end and excellent taste start? Looking through Donatella Versace’s opulent Milan apartment—the ironic queen of all things blond—raises a lot of concerns, one of which is this. With a lengthy history of serving as the house of Versace’s inspiration and eventually designer, she has done for fashion what Jayne Mansfield did for movies: mix equal amounts peroxide, bright pink, and leopard, then press the frappe button. Yes, and don’t close the lid.

While Ms. Versace may be able to respond to such a complex topic herself, her apartment and recent fashion lines demonstrate that navigating the narrow path between the two can be one of life’s greatest pleasures. The former bad kid sister of maestro Gianni has truly come of age.

These days, visitors waiting for a show can explore the expansive main floor in relative quiet as Donatella is now settled upstairs in a recently constructed suite that was made possible by annexing the flat directly above. The rooms downstairs open out like a time machine, telescoping back to 1986, the year Donatella and her then-husband Paul Beck purchased a tiny apartment in the stunning, old building covered in ivy as their first real home. “It was incredibly powerful when I first saw it,” she recalls. And I adore anything strong. The elevator is amazing; it makes me think of the one in Suddenly, Last Summer.

The couple hired the office of famed decorator Renzo Mongiardino to remake the place—the dining room’s mural and blue-and-white tile work still shine, subtle yet showy, almost 20 years later. They called in the same team as their family matured (daughter Allegra is now 19, and Daniel is 15), and they expanded into the apartments next door. The arched and coffered ceilings and geometric floor tiles that are a Mongiardino trademark unify the space, linking both the designer’s and the decorator’s styles. But like Belle Poitrine, the heroine of Patrick Dennis’s brilliant satire Little Me, who one-ups the all-white decor that Syrie Maugham creates for her by having it sprayed pale pink, Versace has definitely gone where no Renzo man has gone before, and quite triumphantly. “I’m not a minimalist,” says Versace, who state the obvious with obvious glee. “But still, my needs and desires have become more simple.”

Simple is, of course, a relative term. For example, the pale pinks and purples of the small living room on the main floor, now used by her children, are a testament to the sophisticated palette that Versace is capable of—as is her latest collection, a desert-hued fantasy. Likewise, the printed velvets that grace the main living room’s Knole sofas bring opulence to a dazzlingly new height that nonetheless manages, even in their savage jungle-beat take on neoclassicism, a certain symmetry and poise.

But if downstairs is more in the style she embraced in the past, when she was in an aesthetic pas de deux with her brother, her new suite, which includes two bedrooms, a living room, a media salon, and a massive bath, is where the real Donatella can stand up.

“You see my evolution more upstairs,” she says. “It’s eclectic. I like modern art and classic furniture.” Indeed, while her favorite colors of black and gold are much in evidence, the restraint downstairs seems to vanish into gestures of sheer girlish enthusiasm: leopard spots on blue velvet brocade! a bathroom as big as the Ritz! “I keep telling them it had to be bigger,” she recalls, laughing. “Most people would think it was huge, but for me it can’t be big enough.” Even after it was finished, she insisted that they make it bigger again, and then, on top of that, add a wall of mirror. “Finally, I’m satisfied.”