Advent a time of penance? That's not true. Where did you learn it?The use of the violet color can surely give that wrong idea. But if you read the liturgical books... you won't find this issue as the central aspect of Advent.
It goes without saying that Advent is not Lent.But yes, read the liturgical formulae. Remember that Christmas Eve is a fast day (and if it fall on a Sunday, the fasting shall be anticipated on Saturday)."Sanctify yourselves, O ye children of Israel, and be ready: for on the morrow the Lord will come down!"
Whilst Christmas Eve may be the ideal time to put up the decorations, I think things can very reasonably be stretched back to Gaudete Sunday (3rd of Advent).I do strongly object though to the secular habit of putting up decorations in November - or even of selling them in the shops before Halloween is even over. The shops should not be selling Christmas decorations until at least 1st December.
Initial decorations for Advent go up today, i.e. the day on which we sing I Vespers of I Sunday Advent.Some decorations will go up on St. Nicholas Day. A few more go up on St. Lucia's Day. Tree goes up, in our home, on Immaculate Conception and doesn't come down until Candlemas.And this year we'll mark the Greater Ferias and the Ember Days as our oldest is finally cognizant of such things.We've tried decorating on Christmas Eve but with a Feast of Seven Fishes and Midnight Mass, it's just too much. So we spend the Advent season preparing for the Nativity.