(informal) Happy, positive things (sometimes with a connotation of unrealistic expectations).
2011, Karen Kingsbury, Found (page 236)
[…] she saw those words these days, and it was easy to take them lightly, to think that God was saying life would be all sunshine and rainbows, good plans and easily answered prayers.
2011, Joe Quinn, Camille Thompson, College of William and Mary 2012: Off the Record
The students are of an astonishingly high quality, it's very hard to find an uninteresting professor, the campus is beautiful, the night life is fun and the campus community is overall really strong. That being said, it's not all sunshine and rainbows.
2013, Victor D. Franco, Unleashed
ELVA: You know, you think everything is lovely. You're a happy, optimistic uni-canary exploding with sunshine and rainbows—go tweet up another tree with that.