Rumer Willis Back on Beach in (Blue) Bikini

By Linda Marx

11/09/2012 at 12:00 PM EST

Life's a beach, all right.

After showing off her bikini bod in Maui last weekend, Rumer Willis and boyfriend Jayson Blair hit the sand a few thousand miles away in Miami Beach, Fla., Thursday.

Rather then the little white number she sported in Hawaii, Willis wore a great-looking blue bikini, noting of the day's weather: "It is really cold here. I wasn't expecting it."

That night, Willis's outfit was something more modest. With her long hair flowing down her back and a long white dress, black bra and flat shoes ("more comfortable," she noted), she entertained a crowd of 800 locals and guests who gathered for the grand opening of the SLS Hotel South Beach.

RELATED: Rumer Willis Stuns in Bikini While Vacationing in Hawaii

Said one guest: "Jayson was so caring and cuddly with Rumer before she performed. They were standing by an elevator nook and he was helping her get ready, giving her confidence, being super supportive. When she sang, he stood in the front row and took pictures."

As for Rumer's personal take on the evening, she told PEOPLE that her parents, Demi Moore and Bruce Willis, are totally supportive.

"My family is behind me with my music," said Willis, 24. "They know it is just another facet of my life."