Dogi. There is no Japanese word "Gi". If you're going to use Japanese terminology, you really ought to use correct Japanese. It reflects upon your attitude toward training as a whole - do you study the technique kote gaeshi (for example), or "that wrist-twist thing". Coloured belts. Coloured dogi. Other garments; hakama, hoi, tabi... even hachimaki! You do whatever your style dictates. It may be redundant to point out, but your organisation's choices of uniform can reveal a lot about the way the organisation "thinks". For any uniform, I would suggest that the design serves just a few purposes; allows a participant as great a range of movement as the activity requires, covers a participant for modesty, protects a participant from harm, eg. friction burns eek, standardises the appearance of students to allow easier comparison, identifies the group to which the student belongs. Have I missed any? There are many solutions, even for the most common roles (think how many answers there are for "what does a soldier wear?"), but they'll all need to match the criteria I listed above.