MILWAUKEE - Colbie Caillat is standing in the middle of her tour bus, holding her iphone and scrolling through pictures of her beloved dogs.

“This is Annabelle,” she says pointing to a picture of a lab mix. “Taupe is here in the middle. That’s Roxy.” She goes on to say that Roxy is the only one of the three shelter dogs still living.

“Roxy is a mixture of a border collie and a rotweiller and she loves to play golf with my dad,” she says with a giggle that belies her superstar status.

Colbie Caillat remains, by all appearances, a regular 23-year-old woman. She is star-struck by her touring partner, John Mayer but misses her family in California. She approaches every experience of her musical career with a wide-eyed, self-effacing enthusiasm.

“The weather is crazy,” she says breathlessly about her first time in Milwaukee. “One minute it is pouring and then the sun comes out.”

It is refreshing to meet a star performer who is clearly having so much fun. A year ago, Colbie was an unsigned Internet sensation. Her music was posted on her MySpace page and developing a large following.

“I put my songs up, I grew a fan base over like six months,” she says now seated on a seat in the bus with her long legs tucked beneath her. “And, then I got noticed by record labels and got a record deal.”

Her Summerfest performance Wednesday night marked the start of her summer tour opening for the Grammy-winning Mayer.

“When I signed my record deal, I was asked who I’d most like to tour with,” she says. “I said I’d love to tour with John Mayer. Now, a year later, I am.”