Tuesday of the First Week of Advent
This guidance from Church Year:

3. Why does my church use the color blue during Advent?
Good question. We have heard many reasons why blue is now a popular Advent liturgical color. One is that blue symbolizes the pre-dawn light. Another reason is that blue is the color of the Blessed Virgin Mary, and the use of blue for Advent may come from this. A third reason is that many churches are trying to distance themselves from the penitential nature of past Advent celebrations, and blue is as close as you can get to violet without being violet. Also, in many places the purple dye used to make Advent vestments and linens was closer to a blue-violet hue than straight violet. Possibly, this eventually led churches in many regions to adopt blue as an Advent color. The last possibility is that blue is a pretty color and offers more variety of color to the limited number of liturgical colors. Regardless, in the Catholic Church, blue is not an approved liturgical color, for Advent or any other season, and it should not be the primary color in any Catholic liturgical celebration.

None of the reasons cited above are valid of course. It is not for us to re-invent the litugry of our own accord. GIRM 346 specifies the following colors for vestments: white, red, green, violet, black (as an option for funeral services and Masses for the Dead), rose (Gaudete and Lætare Sundays), and gold/silver (as an alternative for solemn days).

I’m not sure if the GIRM says anything about Advent wreaths, but the Book of Blessings for the US, ¶1510, mentions only violet, white and rose. We’ve got blue candles, and I could not talk anyone out of them. Why is it so hard for some people to do things right?

The next time this happens, I will say, “If you’re going to go all Protestant on me, I may as well go back to the Baptists where I came from.”