Judo is unique in that your equipment (Judogi) is actually for your opponent’s use. It’s important for the judo gi to fit properly. The following video provides a quick overview of the fit requirements.
Some tournaments require every contestant to have both a white and a blue judo gi. Which color you wear for a specific match, will depend on the order in which you are called for your match. The first contestant called wears a White gi and the second contestant called wears a Blue gi.
Not all tournaments require contestants to have both white and blue gis. Some tournament rules either state that a blue gi is optional or they do not mention a blue gi requirement. In both cases, all contestants can wear a white gi. The contestant on the Blue side will wear blue or colored sash to signify their side.