liturgical colors establish a climate ..Law and ..Gospel
Color allows us to see Light
white.red.green.violet.black.blue.scarlet.gold.
Advent--BLUE(BLUE-the color of the sky-helps convey that powerful message. Our Christian faith rests on the hope that Christ, who came in history assuming our flesh, will also return on the last day of time from that same blue sky he ascended long ago.)
Side note, BLUE is a modern change to the Advent color. Historical tradition indicates PURPLE; penitence.
Introduced by the RCC as BLUE is Mary’s color.
Blue is not a liturgical color.