We follow the Japanese Ki Aikido tradition of mudansha (those who have not yet attained first dan or first level black belt) wearing only white belts, not coloured belts.
There are some other schools within our organisation even in Australia who do use a coloured belt system, but it is just an ornamental difference, and all the dojos teach the same curriculum and have exams with the same criteria.
Our mudansha students may all be girt in white belts, but of course there are differences in ability levels. One person may be a real newbie and another may have several years of practice and be on the verge of going for their black belt!
Also, people get to wear the hakama, the pleated, VERY baggy, skirt like samurai pants when they reach black belt. This is good motivation to work hard for your black belt – the hakama looks extremely cool and feels even better.