A judogi (judo uniform) consists of a joi (judo top), shitabaki (judo pants), and obi (belt). One competitor wears a white uniform, the other wears blue. Traditionally both wore white, but in 1997 the International Judo Federation officially decided to use blue judogi.
This was to make it easier for spectators to distinguish the competitors. It is now easier to see what each is doing when one pins the other to the floor. Blue judogi were first used at the 2000 Sydney Olympics, and colored judogi have become the standard at the World Championships and other major tournaments.
Photos: (from left) The newly introduced blue judo uniform; the traditional white judo uniform (Mizuno Corporation)