Advent used to be a solemn season of preparation. Over time, it went from being "Lenten" to "Lent-like" to (my fave) "semi-penitential" to "If we can get the decorating out of the way and plan at least a couple of shopping runs, we might be able to get in a Christmas pageant or that lessons & carols thingy."
In other words, we replaced religious heaviness with financial, personal and family exhaustion.
The third Sunday of Advent, like the third Sunday of Lent, developed special themes and symbols as a practical spiritual response to the weariness and discouragement that can set in during a solemn season. Hence the rose (no, not "pink," guys) candle on the Advent wreath or even rose colored vestments for the service on the third Sunday.
I found a decent explanation of the tradition here. I leave it to you, dear reader, to reclaim the rejoicing.
There's a lovely Advent meditation in music here.
And there's this,
Jesu, joy of man's desiring
Holy wisdom, love most bright
Drawn by Thee, our souls aspiring
Soar to uncreated light
Word of God, our flesh that fashioned
With the fire of life impassioned
Striving still to truth unknown
Soaring, dying round Thy throne