Tang Soo Do uses the colored belt system that was instituted by Judo´s founder Jigoro Kano and popularized in Karate-do by Gichin Funakoshi. However, minor deviations according to organization and/or individual school are commonplace. One differentiating characteristic of the Moo Duk Kwan style is that the black belt, or dan rank, is frequently represented by a midnight blue belt (some Chung Do Kwan schools also have adopted this custom) for students who attain dan rank. The reason for the midnight blue belt is the belief in Korean culture that black symbolizes perfection. As no one is perfect, the belt for the dan rank is a midnight blue color. It was also a belief of the founder of Moo Duk Kwan, Hwang Kee, that black is a color to which nothing can be added, thus blue signifies that a dan holder is still learning.