This was inspired by a Pepsodent toothpaste commercial
with the jingle, "You'll wonder where the yellow went when you brush your teeth with Pepsodent." According to group member Charles Patrick, he was in a store looking at sheet music for a different song called "Book Of Love" when the jingle came on the radio. He got the idea to combine the title with the melody from the jingle, turning "You'll wonder where the yellow went" into "I wonder, wonder who."
He took the idea to two of his fellow Monotones, Warren Davis and George Malone, and they completed the song.