Yellow Pigs Day, held annually on July 17, is a humorous celebration created and observed by mathematicians at Hampshire College and HCSSIM. The day is marked by exchanging gifts relating to yellow pigs or mathematics, singing yellow pig songs, and playing Ultimate.
Yellow Pigs Day was started by Michael Spivak and David C. Kelly. Spivak’s published books include easter egg references to yellow pigs, and Kelly maintains an extensive collection of yellow pigs. In 2006, Hampshire College held a Yellow Pig Math Days conference, as part of the Hampshire College Summer Studies in Mathematics program.