White clothing is traditionally worn in Brazil's New Year's Eve celebrations to symbolize peace.
The custom is especially visible on beaches, where large crowds gather for Réveillon festivities. White is associated with peace and renewal, and many celebrants combine white clothing with other rituals, such as offerings or flowers connected with Afro-Brazilian religious traditions.
Rio de Janeiro's Copacabana Beach hosts one of the world's largest New Year's Eve gatherings. Fireworks are launched over the water, and people often make wishes while facing the sea. The clothing custom is widespread, but individual people may also wear other colors for particular hopes, such as prosperity or love.
White is therefore the canonical answer for the peace symbolism, not a rule that every Brazilian must wear it. Brazilian New Year's Eve customs vary by region, family, religion, and personal preference.