Not quite Rastoff,
Around 1930 the Kodokan created a new belt to recognize the special achievements of high ranking black belts. Jigoro Kano chose to recognize sixth, seventh, and eighth degree black belts with a special obi made of alternating red and white panels (kohaku obi). The white color was chosen for purity, and red for the intense desire to train and the sacrifices made. The colors red and white are an enduring symbol of Japan, and they have been used in Judo since Jigoro Kano started the first Red and White Tournament in 1884. The kohaku obi is often worn for special occasions, but it is not required to be worn at any time and the black belt remains the standard for all the yudansha ranks. In 1943 the Kodokan created the optional red belt to recognize 9th and 10th degree yudansha.
Other colored belts for students who had not yet achieved black belt originated later, when Judo began being practiced outside of Japan. Mikonosuke Kawaishi is generally regarded as the first to introduce various colored belts in Europe in 1935 when he started to teach Judo in Paris. He felt that western students would show greater progress if they had a visible system of many colored belts recognizing achievement and providing regular incentives. This system included white, yellow, orange, green, blue, and purple belts before the traditional brown and black belts.
The Judo practice uniform and belt system eventually spread to many of the other modern martial arts, such as aikido and karate, which adapted them for their purpose. Karateka in Okinawa didn't use any sort of special uniform at all in the old days. The kyu/dan ranking system, and the modern karategi (modified judogi) were first adopted by Funakoshi in an effort to encourage karate's acceptance by the Japanese. He awarded the first shodan ranks given in karate to Tokuda, Otsuka, Akiba, Shimizu, Hirose, Gima, and Kasuya on April 10, 1924. The adoption of the kyu/dan system and the adoption of a standard uniform based on the judogi were 2 of the 4 conditions which the Dai-Nippon Butokukai required before recognizing karate as a "real" martial art. If you look at photographs of Okinawan karateka training in the early part of this century, you'll see that they were training in their everyday clothes.
Promotion requirements for each rank vary according to the sensei and the national organization that you are affiliated with. There is no worldwide standard for each rank, although it is generally accepted that a blackbelt has had many years of practice...

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Retired Marine Gunny