The Chasuble is the outermost sacramental garment of priests and bishops, usually decorated. It is only worn for the celebration of the Eucharist. It corresponds to the Orthodox phelonion.
READ BELOW FOR APPROVED COLORS OF LITURGICAL VESTMENTS:
GREEN, WHITE/OFF-WHITE, RED and PURPLE are the four most common chasuble colors.
This is an excerpt from the English translation of the Institutio Generalis Missalis Romani.
As to the color of sacred vestments, the traditional usage is to be retained: namely,
a. WHITE/OFF-WHITE is used in the Offices and Masses during the Easter and Christmas seasons; also on celebrations of the Lord other than of his Passion, of the Blessed Virgin Mary, of the Holy Angels, and of Saints who were not Martyrs; on the Solemnities of All Saints (November 1) and of the Nativity of Saint John the Baptist (June 24); and on the Feasts of Saint John the Evangelist (December 27), of the Chair of Saint Peter (February 22), and of the Conversion of Saint Paul (January 25).
b. RED is used on Palm Sunday of the Lord's Passion and on Good Friday, on Pentecost Sunday, on celebrations of the Lord's Passion, on the feasts of the Apostles and Evangelists, and on celebrations of Martyr Saints.
c. GREEN is used in the Offices and Masses of Ordinary Time. (Green is the most used color).
d. VIOLET or PURPLE is used in Advent and of Lent. It may also be worn in Offices and Masses for the Dead. Besides violet or purple, white vestments may be worn at funeral services and at other Offices and Masses for the Dead in the Dioceses of the United States of America.