Doctoral cap design color

Quick answer：

The design color of a doctoral cap typically varies among institutions. It usually represents the field of study or the academic tradition of the university. For instance, in the United States, doctoral caps are typically a flat, round shape known as a 'mortarboard,' with a tassel that can be worn on either side of the cap depending on the field. The color can range from simple black, which is the most common, to colors specific to different disciplines.