Belt systems vary by school and discipline. However, many of them share common roots. They are primarily designed to allow the instructor to determine a student's skill level, and they provide goals for students to achieve.

Traditionally, belts were dyed when a new rank was acheived. Now, belts are usually purchased either before or after a rank has been acheived.

It should be noted that a belt color is not always a guage of a person's knowledge. For example, it is common for purple belts to leave a discipline and begin a new discipline. It is also possible that schools may pass students who are not necessarily ready to be advanced in rank. It is also possible that the person has simply purchased a different rank color, or their school uses a completely different ranking order.

White
The color white signifies innocence, as that of the beginning student who has no previous knowledge of Karate

Yellow / Gold
The beginning student begins to create a firm foundation in Karate. This foundation must be solid, and so the student should work seriously and hard.

Orange
Symbolises changes and warnings. The seed of the plan is beginning to grow roots, and the student begins to adapt to changes. The student has the foundations, but not discipline, which can lead to frustration and anger. Through constant practice and focus, the student will grow.

Green
Green is the most critical period for the karate student, because if the roots and foundation have not been secured, the student will not produce the needed fruits to continue the growing process. A green belt student is both dangerous to himself and others.  He has just enough knowledge to get into trouble.

Purple
The color purple represents the changing sky of dawn, as once again the student undergoes a new change and prepares for the transition to advanced student. The student discovers that he must begin to focus less on himself and more on helping others.

Blue
The color blue represents the sky and water. Students will learn to draw power up from the earth and begin to leave the ground. Their techniques will begin to flow like water.

Red
The color of blood signifies rage and danger, but also courage. The red belt is a sponge, always seeking to learn, and is the hardest working student in the dojo. The red belt enjoys explaining new things to lower ranks. However, the color of blood signifies danger and is a warning to the student to temper her newly found skills and techniques with control and wisdom. 

Brown
The color of rocks and earth, brown signifies the ripening of skills and technique, the brown belt student becomes fully aware of ki and can use the elements to channel that energy. At this level, all techniques have been learned and the student begins to perfect those techniques and adapt them to his style

Black
The foundation is solid and the journey begins as Shodan (First Step) is completed. The student now continues to perfect skills and absorb knowledge. The opposite of white, black is the symbol for discipline and maturity. A person who acheives Shodan is now ready to become a true student of Karate.