Today the color belts in any system of the arts keep changing.
Don't misunderstand me though. There are some dojo's that keep to there color sequence, every dojo is different in this.
Frankly to me they are only important, so I can tell the students progress.
For the younger ones, it gives them incentive to practice hard.
For the older ones, they already know that they are examples for the ranks under them. Showing respect for the higher ranks they will learn discipline.
My color sequence are from the light colors beginners, to dark colors experience ones.
Ryu ranks...white, yellow, orange,green, blue, brown 1, brown 2. Dan ranks from 1 to 10 with a stripe added on the belt as they progress in the art and teaching responsibilities. The art begins here.
Any higher than 6th degree, roku dan, they must spread out the art to other locations, if they can with honors.
I hope this gives you some idea of the color system.