What is Here Comes That Rainbow Again about?

Here Comes the That Rainbow Again is actually from a chapter from John Steinbeck's "The Grapes of Wrath". In one of the secondary chapters/interludes from the story, it takes place in a diner and the events that transpire in the song are what happens in the book as well. A fantastic book and definitely one of the most down to earth/"there's hope for humanity" chapters I ever read.