General Instruction of the Roman Missal, IV: § 335-345.
335. In the Church, which is the Body of Christ, not all members have the same function. This diversity of offices is shown outwardly in the celebration of the Eucharist by the diversity of sacred vestments, which must therefore be a sign of the function proper to each minister. Moreover, these same sacred vestments should also contribute to the decoration of the sacred action itself. The vestments worn by Priests and Deacons, as well as the attire worn by lay ministers, are blessed before being put into liturgical use according to the rite described in the Roman Ritual.
336. The sacred garment common to all ordained and instituted ministers of any rank is the alb, to be tied at the waist with a cincture unless it is made so as to fit even without such. Before the alb is put on, should this not completely cover the ordinary clothing at the neck, an amice should be used. The alb may not be exchanged for a surplice, not even over a cassock, on occasions when a chasuble or dalmatic is to be worn or when, according to the norms, only a stole is worn without a chasuble or dalmatic.
337. The vestment proper to the Priest Celebrant at Mass and during other sacred actions directly connected with Mass is the chasuble worn, unless otherwise indicated, over the alb and stole.
338. The vestment proper to the Deacon is the dalmatic, worn over the alb and stole; however, the dalmatic may be omitted out of necessity or on account of a lesser degree of solemnity.
339. In the Dioceses of the United States of America, acolytes, altar servers, readers, and other lay ministers may wear the alb or other appropriate and dignified clothing.
340. The stole is worn by the Priest around his neck and hanging down in front of his chest, while it is worn by the Deacon over his left shoulder and drawn diagonally across the chest to the right side, where it is fastened.
341. The cope is worn by the Priest in processions and during other sacred actions, in accordance with the rubrics proper to the individual rites.
342. As regards the form of sacred vestments, Conferences of Bishops may determine and propose to the Apostolic See adaptations that correspond to the needs and the usages of the individual regions.
343. For making sacred vestments, in addition to traditional materials, natural fabrics proper to each region may be used, and also artificial fabrics that are in keeping with the dignity of the sacred action and the sacred person. The Conference of Bishops will be the judge of this matter.
344. It is fitting that the beauty and nobility of each vestment not be sought in an abundance of overlaid ornamentation, but rather in the material used and in the design. Ornamentation on vestments should, moreover, consist of figures, that is, of images or symbols, that denote sacred use, avoiding anything unbecoming to this.
345. Diversity of color in the sacred vestments has as its purpose to give more effective expression even outwardly whether to the specific character of the mysteries of faith to be celebrated or to a sense of Christian life’s passage through the course of the liturgical year.
Explanation of Vestment Colors for the Latin Rite
General Instruction of the Roman Missal, IV: § 346-347.
346. As regards the color of sacred vestments, traditional usage should be observed, namely:
a) The color white is used in the Offices and Masses during Easter Time and Christmas Time; on the Solemnity of the Most Holy Trinity; and furthermore on celebrations of the Lord other than of his Passion, celebrations 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 St. John the Baptist (June 24 ); and on the Feasts of St. John the Evangelist (December 27), of the Chair of St. Peter (February 22), and of the Conversion of St. Paul (January 25).
b) The color red is used on Palm Sunday of the Lord’s Passion and on Friday of Holy Week (Good Friday), on Pentecost Sunday, on celebrations of the Lord’s Passion, on the “birthday” feast days of Apostles and Evangelists, and on celebrations of Martyr Saints.
c) The color green is used in the Offices and Masses of Ordinary Time.
d) The color violet or purple is used in Advent and Lent. It may also be worn in Offices and Masses for the Dead.
e) Besides the color violet, the colors white or black may be used at funeral services and at other Offices and Masses for the Dead in the Dioceses of the United States of America.
f) The color rose may be used, where it is the practice, on Gaudete Sunday (Third Sunday of Advent) and on Laetare Sunday (Fourth Sunday of Lent).
g) On more solemn days, festive, that is, more precious, sacred vestments may be used even if not of the color of the day.
h) The colors gold or silver may be worn on more solemn occasions in the Dioceses of the United States of America.
347. Ritual Masses are celebrated in their proper color, in white, or in a festive color; Masses for Various Needs, on the other hand, are celebrated in the color proper to the day or the time of year or in violet if they have a penitential character, for example, nos. 31, 33, or 38; Votive Masses are celebrated in the color suited to the Mass itself or even in the color proper to the day or the time of the year.