The Purple Cow is Williams' mascot, its creation inspired by the infamous poem by Gelett Burgess:
I never saw a Purple Cow,
I never hope to see one;
But I can tell you, anyhow,
I'd rather see than be one.
This was later followed by a sequel:
Ah, yes, I wrote the "Purple Cow"—
I'm sorry, now, I wrote it!
But I can tell you, anyhow,
I'll kill you if you quote it.
According to the photo archives of the House of Local History in Williamstown: Farms still existed right up to the edge of campus a hundred years ago. This included a farm next to Weston Field. One night several young men were feeling adventurous and proceeded to paint the poor cow purple.
The Purple Cow is also the name of Williams' first humor magazine.
See The Cow.