i really don't know what the rules are for other aikido organizations, but my dojo is an independent dojo and we have colored belt rankings as follows:
we have over 200 students with our club, and everyone goes to different dojos throughout the state. I think the colored rank system is good because it lets the numerous instructors that we have in our club know exactly where you are in your training if you were to visit another Ronin Bushido dojo. I like Mr. Ellefson's statement about the colored ranking system being about safety. That was great.
Even though the Hakama is a traditional thing for everyone to wear, i think that they should only be worn by people who are Shodan and higher. To me, the Hakama has authority written all over it, and i would feel unworthy and incompetent if i wore a Hakama.