The first day of Advent marks the first day of the Liturgical Year in the Catholic Church. Like all Church seasons, it is denoted by a color. This one is marked by my favorite: purple! Purple signifies both the sovereignty of Christ (his Kingship - hey, it is a royal color!) and penitence. If you want to be very technical, the purple of Advent is deeper and darker than the purple of Lent (of course, we get a liturgical break on the 3rd Sunday of Advent, but that's for another post!).
Image Credit: UCC
P.S., it is not the Christmas season yet. I know this will come as a shocker to a lot of people, but Christmas doesn't start until December 25th. It ends on the feast of the Baptism of the Lord (which has been moved to a fixed date on the Sunday following the feast of Epiphany, the Sunday closest to January 6th). So, if you're a Catholic, or any devout Christian, hold off on the Christmas decorations and enjoy the season of Advent.
The first week we Wait.
The second week we Prepare.
The fourth week we Behold.
Then, we celebrate the birth of our Savior!