In any martial arts, it is easy to distinguish who has become a skilled practitioner, and who is just starting out. Almost all martial arts use belts, long, thick cotton fabric, in order to reward those who have achieved a higher ranking, as well as to easily show who deserves the most respect in the dojo.
It is impossible to distinguish which color means which rank, as each martial art is a bit different. Traditionally, though, the white belt is for a beginner, and the black belt is for an expert. Depending on the martial art, black belts can take years, or decades, to obtain. A large amount of the time, a black belt signifies that the student is ready to become the teacher. This is one of the highest forms of praise that any martial artist can hope to receive. There are ranks above and beyond a black belt in most martial arts.
As with any aspect of martial arts, there is a huge amount of different quality you can choose from. Most belts in martial arts are made of cotton, but some are made of silk. The higher the quality of the belt, the longer you know it will last.
If you have moved up in the ranks, you might want to consider getting a belt holder and display. This allows your belts to be safely folded, while displaying your achievements.