Non-confrontational, agreeable to everyone, if used as an adjective. By itself, it is an interjection that roughly means "hey, everybody be nice and get along!"
"Bill wanted chicken for dinner, but Martha only wanted salad. As a puppies and rainbows solution, they had a chicken caesar salad."
Adam: "Wake up, David! If we don't delay the launch of the product, it's going to be a complete disaster!"
Robert: "Whoa whoa, guys. Puppies and rainbows!"