The Simpsons season 21 episode 13
Episode title: The Color Yellow
When Miss Hoover asks her students to research their family history, Lisa is horrified to discover that most of her ancestors were bad people – a motley crew of horse thieves and deadbeats. But while rummaging through the attic, Lisa happens upon a diary kept by her ancestor, Eliza Simpson. As Eliza’s story unfolds, Lisa learns that her family was part of the Underground Railroad, a group that helped slaves escape to freedom. Eliza recounts liberating a slave named Virgil, but when Lisa presents her findings at school, some of her classmates refute it, leaving Lisa determined to exonerate her family’s name.