If I understand things correctly the colored belt system is a western invention. Our mindset sorta requires that we have incremental goals to chase after. As corny as it sounds...it's the journey not the destination that matters most to me.
On a related note...why are there different requirements for the hakama in some styles for men and women?
Others have touched on the kyu/dan system, but from my understanding the reason women are allowed/required to wear hakama is for modesty purposes. In his newest book, Dave Lowry talks about this.
In my dojo it's white up to 2nd kyu and then brown until shodan. Males can only wear hakama at shodan and above