In traditional Aikido there are two belt colors: white belt and black belt.
The white belt goes from 10th Kyū (or Jikkyū) to 1st Kyū (or Ikkyū).
The black belt goes from 1st Dan (or Shodan) to 10th Dan (or Jūdan), but I think that you already know those things.
Wearing a white belt means that you are still a beginner or a learner.
I found a site that explains why Aikido belts are a modern invention: http://www.martialartsguy.com/aikido-belts/