Answer: The color rose is only occasionally used liturgically, and it represents joy. Halfway through the otherwise muted season of Advent, we express the joyful aspect of anticipating the Lord’s coming. You can hear the theme of joy and rejoicing throughout the readings and prayers in the Mass.
The third Sunday in Advent was nicknamed “Gaudete Sunday” long ago. Gaudete means ‘rejoice!’ in Latin, and is the first word in the Latin Mass for that day. If you look up the “entrance antiphon” in a missalette, you will see that it starts out: “Rejoice in the Lord always!” In the Latin that would read Gaudete in Domino semper! Today we usually sing an opening hymn rather than recite or chant the entrance antiphon, but the theme of rejoicing is no less conspicuous now on Gaudete Sunday than in the past.
There is a counterpart to Gaudete Sunday in Lent. Halfway through Lent we celebrate what is traditionally called “Laetare Sunday.” As in Advent, we take a mid-term break from the somberness of the season for joyous anticipation. Laetare Sunday also takes its name from the entrance antiphon of the day, whose first word is a Latin synonym also meaning, “rejoice” or “be joyful.” This is the other time you may see liturgical use of the color rose.