When most Asian Martial Arts were in their developmental stages (from the time of Christ to around 800 A.D.), systems of belt/color ranking did not exist. School format was usually very informal, and most practitioners learned from Buddhist monks or through the family (father-to-son). Even regimented Martial Arts training in the military, such as the Hwa-Rang-Do of Korea's Silla and Koryo Dynasties (567 A.D. to 1392 A.D.) did not have a system of ranking (for their Martial Arts classes, at least).
Classes were usually small enough that everyone knew who the instructor was...thus the instructor dressed no differently than his students. Everyone wore belts that were colored white, for the express purpose of keeping their gi-tops or doboks from flying open.
However, even though they never had belt tests, the color of their belts did change. As the student began to work hard, his sweat would pour out, and stain his belt from white to a dim-yellow. As time passed, the sweat stains were joined by grass stains attained from rolling on the ground, and thus the belt would appear to have a greenish-tint to it. As the student continued to acquire grass stains, he would also continue to sweat, forcing a color change of green and yellow at the same time, thus the belt would appear to be blue. Dirt would also begin to collect on the belt, as student progressed, sometimes creating the illusion of brown. As the student advanced, and became better and better, his instructors and opponents would push him harder, and frequently injure him to the point of bleeding, which would cause the belt to show qualities of a dark red.
Ultimately, when the belt was stained to the point that no color change would occur, it became a dark-gray or black. This change would take years to occur, and signified the wearer as an advanced practicioner. But this was not the last change to take place. Eventually, after many years, the material on the belt itself began to wear away, and it would slowly change from black, BACK to white. A person whose belt had endured this change, was revered as a master, and respected by warrior and commoner alike.
This is the reason for the traditional rule (found in most schools) which states that a student must NEVER wash his/her belt. To do so, would wash away the significance of the student's hard work and spirit. This is also the reason that most Black Belts have a work-out belt, in addition to an embroidered Black Belt. This way, they can wear the same belt from the time they are a Black Belt, on until the day comes that they can no longer work out. If they work hard enough, their black workout belt will begin to show signs of wear and tear, and eventually peel back to white, just like the belts of the original masters.
Around the late 1800's to early 1900's, belt/rank systems became more-frequent. Eventually, by the time that most Asian Martial Arts came to the US (mid 50's to late 60's), most ranking systems had been in place for a significant amount of time. The most common color scheme started students as a White Belt, followed by colors that became increasingly-darker, until the Black Belt was attained. Some styles have varied from this, as some schools of Karate opted for a Red Belt to be that of a master.
Some styles will also have meanings for each belt, depending upon the system. Now, since belt colors change from place-to-place, we have meanings for every belt color that we could think of. Also, because of the different sequences of rank that are found, these are listed in no particular order.
NOTE- It should be noted that the colors/meanings found here reflect what is common among most Korean/Japanese styles of Martial Arts. Chinese Styles are vastly different in both meaning and order (for example, in some styles of Chinese Martial Arts, a White Belt or Sash signifies the highest rank, instead of Black).
If we are missing any that you know the meaning to, PLEASE LET US KNOW.