The belt system of Taekwondo came from the practice of old fashioned clothing.
Originally, there were only one belt, and it was like that there was no belt system. The basic belt was white because the dyeing skill was not much advanced at that time.
As a practitioner continues his exercises, his belt got dirtier and dirtier, up to black. Although the clothes could be washed but the belt was a trivial thing so that people didn't intended to wash it. And the degree of dirtyness of belt came to represent the amount of practice, thus the rank. So, they say, white belt appear again after black belt, because after got dirty, the belt will be so old that it shows its inside off, white.
Later red belt appeared between white and black. Why? The red belt came from the blood of practice. As practitioner shed blood during the practice and it made belt red. So the traditional Taekwondo system had only three colors of white, red, and black.
Later again, other colors appeared, for the degrees of three colors had too big difference, and the current practitioners felt difficulty to get motivated by the ranks. That is, another colors was created in order to motivate beginners. The order is like that : white, yellow, green, blue, red, black. Some masters added another colors among them, but it is not important.
The essence is that the color of belt shows Taekwondo ability not by the money or artificial system, but by its natural changes of life. No efforts and time, no Taekwondo. The ranks of belts comes from the amount of time he has wasted in practicing.
You cannot the true Taekwondo with money, but only by your sweat and blood. And this is why Taekwondo is valued.