Colbie Caillat's third album, due out this spring, will follow up her aptly titled sophomore effort, "Breakthrough," which topped the Billboard 200 in 2009. The singer sounds as bubbly as ever on "I Do," her latest single and the first taste of the new disc. "I Do" features lighthearted percussion and guitar as well as a swinging melody designed to make listeners tap their toes. Beyond the cheery surface, Caillat's maturation as a songwriter and vocalist is abundantly clear. The lyrics, which focus on love and marriage, are equally adult and adorable, and the singer adds her vocal sweetness to the mix. The sugary pop of "I Do" is hard to hear just once and nicely precedes Caillat's forthcoming album, which should be another cheerfully addictive effort.