There are a lot of myths about the belt ranking system. The most common being is you wear your white belt until it turned black and that is how you obtain a black belt.
Jigoro Kano can be credited with bringing the belt system into modern day martial arts. He is accredited with bringing not only the belt system but resistance-based training as well. He is the founder of Judo and modified jiu jitsu into a resistance based sportive art. Which improved many aspects of what was currently being practiced.
He copied the black belt from swimming. An advanced swimmer in Japan received a black ribbon tied around the waist. He copied that and the beginner was a white belt and an advanced student was awarded a black belt.
The colors came into play some time later. It was a French Judo practitioner that came up with I believe a green belt rank to retain students as many were quitting before black as the European wasn’t as patient as the Japanese and needed to be rewarded.
The American’s being even less patient took it a step further and created many other ranks. Which were then adopted universally around the world with many different colors in different styles. The history on who did what when becomes real muddied as everyone tries to take credit for different colors.
That is the basic history blanketing the martial arts as a whole. I will post a nice summary of the Gracie jiu jitsu belt system tomorrow which is real interesting.