Freshman caps, or beanies, were a common sight on many American college campuses into the early 1970s. Some were skull caps with the school colors and others like the caps at Purdue had brims and other features. The Purdue tradition began with the Class of 1911. The story goes that this particular class, when it arrived in 1907, was distinctive enough that the upper classmen feared that these newcomers would be mistaken for juniors or seniors. The upper classmen forced these "green" fledglings to wear an Eton style cap of the appropriate color. A unique feature to the Purdue caps was the button at the top of the cap. To further distinguish the wearer the color of the button varied depending on what school the freshman belonged. As noted in the 1914 Debris, Aggs wore orange buttons, Civils red, Chemicals purple, Science black, Electricals white, and Mechanicals blue. The class of 1915 introduced green stocking caps or toques for winter wear. At some point the different colored buttons was discontinued and the button was the same color as the cap for all freshman.
1)"Legends Customs" 1914 Debris (West Lafayette, Purdue University, 1914); 344.
Freshman caps in 1958
Source: 1958 Debris, page 6