As legend has it, a white belt was issued at the start of training. The uniform would be washed, but the belt was NEVER washed. It is believed that your belt represents all of the knowledge you gained through your experience. If the belt is washed, then all the knowledge you have gained would be washed away. Over the many years of training and not washing your belt, it eventually turns darker and darker from collecting all of the dirt, blood, sweat, and tears...transforming into a Black Belt.
The NEURON-DO® story of the belts represents the life cycle of the tree. There is symbolism in which the growth of the tree is reflected in the growth of the student. This is an ongoing process that does not stop once Black Belt is achieved. This is also true for your neurons, in which you can continually grow new connections throughout your life and there is even evidence that you can even grow new neurons. Arborization is a term used to describe the growth of new connections between neurons because it looks like the growing branches and roots of a tree.