Each style assigns their own ranks as they please. A certain colored belt in one school doesn't mean the same as the same color belt in another school. Some schools don't even have belts. Some don't even have ranks. Don't let the rank game distract you from what is really important.
Some schools belong to world-wide organizations.
These have the advantage that you can transfer your rank to another member school. They usually have the disadvantage of dues that each student must pay to the organization. Often there are two or more rival organizations for a given style. The politics involved in such things are extremely involved. In deciding on a school, I would tend to place little significance on their organization, and much more significance on the quality of training at that particular school.