In the Catholic church ( which I was brought up in ) purple was used everywhere especially during lent and advent, the season before Christmas.
Here is a little blurb I found, and it relates to royalty and Jesus being "The Prince Of Peace", so the association with purple is used.
The color purple, then, highlights the whole program of the Church's Lenten prayer. The purple shades of Lent focus our attention on Christ's kingship and, more importantly, on the sufferings that perfect His royal dignity and merit us grace, that gratuitous gift of God's own life that transforms our sinful hearts. It is a small sign of Christ's power that the feasting of our eyes on this luxurious color can move our souls to prayer and contrition. In the Redemption, the color purple no longer lifts human heads in earthly pride, but instead it lowers our heads, bends our knees, and brings our fists to our breasts as we plead for mercy. If, for our benefit, Christ effects this conversion in history's use of the color purple, imagine what He wants to do this Lent to the still black parts of our souls.