After coming across a story about a leprechaun and his pot of gold at the end of the rainbow, Curious George learns about real rainbows, the colors they reveal, and the weather that causes them.
When Roy G. Biv, a leprechaun, appears and asks Colleen's help in saving the St. Patrick's Day parade, she offers items of different colors to rebuild his lost rainbow, but is reluctant to part with a special gift from her grandfather.