What is the purpose of rose during Advent?

Why is rose used during Advent in the Advent wreath and vestments?

Advent is a time of penance and so the ordinary liturgical color for Advent is violet. On the Third Sunday of Advent, which is also called Gaudete (Latin, “joy”) Sunday, we also recognize the joyful anticipation of the season that will culminate in the birth of Christ on Christmas by changing the liturgical color to rose. Rose is a “brightening” of the ordinary violet and thus symbolizes joy.