"Customarily the Advent Wreath is constructed of a circle of evergreen branches into which are inserted four candles. According to tradition, three of the candles are violet and the fourth is rose. However, four violet or white candles may also be used” (Book of Blessings 1510).
The rose candle is lit the third Sunday of Advent, for this color anticipates and symbolizes the Christmas joy announced in the first word of the Entrance Antiphon: "Rejoice" (Latin, Gaudete). For this reason the Third Sunday is also called Gaudete Sunday, and rose color vestments are permitted.
The Advent Wreath represents the long time when people lived in spiritual darkness, waiting for the coming of the Messiah, the Light of the world. Each year in Advent people wait once again in darkness for the coming of the Lord, His historical coming in the mystery of Bethlehem, His final coming at the end of time, and His special coming in every moment of grace.
During Advent, family and friends can gather around the Advent Wreath lighting the appropriate candle(s), read from the daily Advent meditation and sing songs. The Church's official Book of Blessings also provides a blessing ceremony for the advent wreath which can be used in the absence of 
a priest.