For most Roman Catholics who only attend Sunday Mass, red can be a rare vestment color, as it is only worn on Pentecost Sunday, Good Friday and on special feasts (such as the feast of the Exaltation of the Cross), when they fall on Sundays during the liturgical year.
Red is also worn on the feast days of martyrs, or for a votive Mass of the Holy Spirit, but few Catholics will witness those days as they typically fall during the week.
Symbolism of red on Pentecost
In the Roman Rite, the Church has chosen the color red for the vestments worn by the priest and deacon on Pentecost Sunday.
Heinrich Stieglitz wrote about this liturgical color in his 1923 book The Church Year, explaining its symbolism:
Red is a warmer and stronger color than white. It glows like fire and signifies heavenly love. The Holy Spirit is Divine Love. He came from heaven in the form of fiery tongues. The hearts of the Apostles burned with holy love. Speech came from the lips of St. Peter in a stream of fire, as it were, and inflamed the hearts of the Jews. The feast of Pentecost therefore is celebrated in red.
The Catechesis of the Good Shepherd similarly teaches children that the color red is the color of great love.
The reference to the fiery tongues comes from the Acts of the Apostles:
When the day of Pentecost had come, they were all together in one place. And suddenly a sound came from heaven like the rush of a mighty wind, and it filled all the house where they were sitting. And there appeared to them tongues as of fire, distributed and resting on each one of them. And they were all filled with the Holy Spirit and began to speak in other tongues, as the Spirit gave them utterance.
Acts 2:1-4
Ever since that fateful day on Pentecost, red has been associated with the action of the Holy Spirit.
Outside of Pentecost, red is most often connected to the shedding of blood, and is one of the reasons why it has been chosen for Good Friday.
While Pentecost does not represent the blood of sacrifice, it does correspond to two other spiritual meanings that the Church has recognized. According to the Catholic Encyclopedia, red “is the language of fire and blood, indicate[ing] burning charity and the martyrs’ generous sacrifice.” With that in mind, red for Pentecost can be seen in reference to the flames of fire that came down upon the apostles, as well as the fire of “burning charity” that arose in them after that day.