Redemptionis Sacramentum: vatican.va/roman_curia/congregations/ccdds/documents/rc_con_ccdds_doc_20040423_redemptionis-sacramentum_en.html
4. Liturgical Vesture
[left][121.] “The purpose of a variety of colour of the sacred vestments is to give effective expression even outwardly to the specific character of the mysteries of faith being celebrated and to a sense of Christian life’s passage through the course of the liturgical year”. On the other hand, the variety “of offices in the celebration of the Eucharist is shown outwardly by the diversity of sacred vestments. In fact, these “sacred vestments should also contribute to the beauty of the sacred action itself”.
[122.] “The alb” is “to be tied at the waist with a cincture unless it is made so as to fit even without a cincture. Before the alb is put on, if it does not completely cover the ordinary clothing at the neck, an amice should be put on”.
[123.] “The vestment proper to the Priest celebrant at Mass, and in other sacred actions directly connected with Mass unless otherwise indicated, is the chasuble, worn over the alb and stole.” Likewise the Priest, in putting on the chasuble according to the rubrics, is not to omit the stole. All Ordinaries should be vigilant in order that all usage to the contrary be eradicated.
[124.] A faculty is given in the Roman Missal for the Priest concelebrants at Mass other than the principal concelebrant (who should always put on a chasuble of the prescribed colour), for a just reason such as a large number of concelebrants or a lack of vestments, to omit “the chasuble, using the stole over the alb”. Where a need of this kind can be foreseen, however, provision should be made for it insofar as possible. Out of necessity the concelebrants other than the principal celebrant may even put on white chasubles. For the rest, the norms of the liturgical books are to be observed.
[125.] The proper vestment of the Deacon is the dalmatic, to be worn over an alb and stole. In order that the beautiful tradition of the Church may be preserved, it is praiseworthy to refrain from exercising the option of omitting the dalmatic.