Just a beginner opinion,goes like:-
I believe those belt meanings go pretty much in the same line with many of the arts that use the classic white-black system.
There at least used to be a TKD site which had slightly detailed explanations on each belt.
You may know this already but I“ll write some.
White belt-displays innocence (of the practitioner who does not yet have experience on one“s MA)
Black Belt-There seem to be plenty of explanations but one "traditional" one is that the belt becomes darker and darker from all the blood,sweat and related dirt you spill during practice.
So it“s kind of a from white to black,I don“t know what those bodily fluids and other stuff has to do with green,red and related belts between

.In some arts like at least part of aikido circles use only three belts-white,brown,black.
So I could suppose they don“t always make a big fuss about belts.Then there are styles like jujutsu where you get belts which include both black and red in one,at very high levels.
Getting even more complex as you see.
They say that Jigoro Kano created the whole system of belts so maybe you should search judo circles,ask questions if someone knows something.
Some say that it was from japanese swimming team“s colours he got it from,while some deny that (so if the first group is right,then you might want to search that swimming thing too

)
And as my last whispers,in TKD and aikido 1.dan (point where you would expect to get a black belt,this may vary in aikido though.In aikido shodan/1.dan rank/BB is considered a start generally) it was explained like "now in this point a student has reached a level of understanding of basic techniques and may start advanced studies" (my major source being that same TKD site) as in aikido.
I hope this helps to a point.
:asian: