Belt Colors
The white belt is, by Corpora, reserved for Knights. That is the only Society-wide reserved belt color.
A tradition started some time ago to use additional belt colors to indicate some relationships. This tradition appears to have started in the Pennsic kingdoms, and spread throughout the Known World from there. First was red belts for squires, then green belts for apprentices, and yellow belts for proteges. Some kingdoms have made these formally reserved, by including a sumptuary law about them in their kingdom laws.
Caid does not reserve any belt color but white.
In Caid, a squire may be given a red belt by their knight, usually with the personal arms of the knight on the chape. But anyone can wear a red belt.
An apprentice may be given a green belt by their laurel, often with the personal arms of the laurel on the chape. But anyone can wear a green belt.
A protégé may be given a yellow belt by their pelican, often with the personal arms of the pelican on the chape. But anyone can wear a yellow belt.
Though do note, if you do wear a specific belt color, people will assume you are of that rank. For example, if you are a fighter who is not a squire, but wear a red belt, don't be surprised if Knights don't ask you to become a squire -- they will think you are already one!