In medieval Europe the caps and gowns worn by the academic community were in black. The color black, the preference of ecclesiastical leaders, was a symbol of authority. This austerity has been retained by modern high schools and universities in the caps and gowns worn at graduation ceremonies. The tassel that graduates transfer from one side of the cap to the other as a sign of their elevation is an outgrowth of the medieval biretta, a tufted square cap appropriated by undergraduates and schoolboys.
Example:
A: Hi, Jane. Graduation is next week. Have you rented your cap and gown yet?
B: You bet! My mom and dad have been taking pictures of me wearing them all week.
A: What do you do to keep your cap on? Mine falls off every time I look up.
B: No problem. Use booby pins and always look down. You never know what you’ll find.
A: Come on, be serious!