This coming Sunday, December 14, is Gaudete Sunday, the third Sunday in Advent. It gets its name from the Latin word gaudete meaning “rejoice”, and it was the first word in the Introit for this day’s Mass . It is on this Sunday that the rose colored candle in the Advent Wreath is lit, and one of two Sundays in which rose vestments (often appearing pink) may be worn.
“The spirit of the Liturgy all through Advent is one of expectation and preparation for the feast of Christmas as well as for the second coming of Christ, and the penitential exercises suitable to that spirit are thus on Gaudete Sunday suspended, as were, for a while in order to symbolize that joy and gladness in the promised Redemption.” (source)
More info here: http://en.wikipedia.org/wiki/Gaudete_Sunday