Re: Same ranks, but different colours?
The color of belts can vary so much, that the only one that matters is the dojo where you're training. Though, worldwide most aikido dojos use white for kyu and black for dan. What's a little more important is what kyu grade you might have at any given point. And if you move to another place, it may or may not be recognized.
Some systems/organizations/dojos may recognize ranks from other places, and some may not.
Just train. : )