There are only two days in the litugical year when rose may be worn, today and Gaudete Sunday in Advent.
How did the custom of rose coloured vestments become established in the Church?
It goes back to the IV Century when the Roman Empress, and wife of Constantine the Great, St. Helena, presented roses of pure gold to the heads of allied countries and important persons which were especially blessed by the Pope on this day. This became known as the Sunday of the Roses. Thus, the custom arose of wearing rose colored vestments which was extended to the whole Church although the custom of giving golden roses died out.