I did a rainbow quilt many years ago. I picked 6 fabrics that were colors of the rainbow. I cut them so that the 6 could fit a 6 1/2 block. I made a rail fence with the blocks.
I did this for the director and his wife for the show my son was in. They were doing the Wizard of Oz and I found a great fabric of Dorothy and the munchkins. It was too pretty to cut so I used that for the back.
Of course everyone knows Dorothy went over the rainbow to get to Munchkin land.