Navy is the basic colour. The title of Warrior is associated with it. These are the most common sehashi. It's common for their uniforms to change in design, but will always retain the basic navy colour, signifying the level of their power.
Cerulean is the second level of power with the title of Champion going along with it. The Champion's uniform is always different from anything they had as a Warrior, though their primary and secondary colours will remain consistent, regardless of their power level.
Bronze is the third level. These sehashi have the title of Hero. It's very common for the uniforms displayed in this level to be somewhat more elaborate than the previous two levels of power. It's not common for a sehashi to progress this far. Most don't make it past Champion.
An off white uniform signifies a Sentinel. These sehashi are not quite as powerful as the Guardians, but are often treated as the same thing. At this stage, they often choose a Guardian name for themselves, though they don't use it. If this stage is achieved, they will always make it to the next level. Very few Heroes make it this far.
A pristine white uniform is the mark of a Guardian. This is generally seen as being the most powerful level possible. Only their primary colour is displayed alongside the white of their level.
A multi coloured uniform is as uncommon as the white Guardian one and those who wear it are known as Celestial sehashi. These are sehashi that have nearly god-like powers and at some point in their planet's history, they were mistaken for such. These sehashi are often so powerful that they skip several of the early stages.
Black uniforms are the rarest and only worn by the most powerful. At present, only three are known to exist. These sehashi are effectively immortal. The one depicted above is so old her name has been lost to all but her. Spirit Guardians are aware of her name as well, though they don't speak it out loud. There is no title associated with this uniform colour. In ancient times it was felt that there was no word strong enough to accurately describe their powers. These are the only sehashi that can outmatch a Celestial.