In East Asian martial arts, the black belt is associated with expertise, but may indicate only competence, depending on the martial art.The use of colored belts is a relatively recent invention dating from the 1880s.
Black symbolizes the darkness beyond the sun, and a person who has been awarded a black belt seeks to gain a deeper and further understanding of the physical and mental teachings of karate.
The "Black Belt" was designed as a way to show competence in the art, not mastery of it. Achieving 1st dan is the beginning of the journey, hence why kyus count down and then dans count up.
To many, the black belt is a sign that one has mastered the art of karate. However, holding a black belt, while a very impressive accomplishment, does not mean that one has reached the upper echelons of karate skills. Once a person tests into the black belt rank, there are still 10 levels that must be accomplished before he will get his final belt.