It's raining, and Colleen is sad. How can her grandfather play his bagpipes in the St. Patrick's Day parade? His music is so beautiful it makes people laugh and cry at once. Suddenly, a leprechaun appears before her. He says he can make the sun come out by creating a rainbow - but to build its colors, Colleen must give up the thing she holds most dear.

A note at the end explains the science of rainbows and the Roy G. Biv naming tradition.