In the old days the white belt was simply dyed to a new color. This repeated dying process dictates the type of belt color and the order of the colors!. The standard belt color system is white, yellow, green, brown, and black. In some Karate school and styles, the color order is white, yellow, orange, green, blue, brown, black.
karate belt colors
Due to the dying process, it is practical to increasingly use darker colors. All of this came about shortly after the second world war, when Japan was a very poor country, and dying the belts to a new color was a cheap way to have a visible, simple and effective ranking system.