Why does the priest wear different colored vestments?

The priest wears different colored vestments to express the spiritual character of each liturgical season or feast. The Roman Rite prescribes white for joy and purity, red for the Holy Spirit and martyrdom, violet for Advent and Lent, green for Ordinary Time, rose on Gaudete and Laetare Sundays, and black for Masses of the Dead. Each color orients the faithful to the mystery being celebrated.

The Meaning of Each Liturgical Color

Additionally, in certain regions such as Spain, blue vestments are permitted by indult for Marian feasts, though this is not part of the universal discipline of the Roman Rite.