A discussion the proper color for tabernacle veils and antependia at Requiem Masses, moved me to do some investigation about Dominican practices. The result was something of a surprise, and nothing about it is found in Bonniwell's history of our Rite.
Since the edition of 1687 edition of the Dominican Missal produced under the direction of the Master of the Order Antonin Cloche, O.P., Dominican vestment colors have been identical to those of the Roman use. Before that date, however, the practice was different. Use of white, red, and green basically followed the modern Roman use, but there were interesting exceptions. On simplex feasts of confessors, where the Roman use was white, the celebrant had a choice between using yellow or green. This use of yellow for confessors is a well-known aspect of the Sarum Rite.
The use of green assimilates, at least in the time after Epiphany and Trinity, simplex feasts to the ferial. This is not surprising, as the Dominican Rite of Humbert (1256) and the middle ages resisted the early modern practice of introducing so many saints' days and raising them in so much rank as to erase the ferial office and even that of Sundays (as was generally the case before the Pius X calendar reform). Indeed, the number of feasts above simplex was very limited in the ancient Dominican liturgy, even Apostles were only semidoubles. Although I cannot find any rubric on it, I suspect that the use of the ferial color was also at least an option on feasts of three lessons. In the 1200s and 1300s confessor feasts with yellow vestments included, among others, Gregory the Great, Benedict, Ambrose, Bernard, and Francis. All were only simplex feasts. It is also interesting that the vestment for the "highest feasts" was to be "the best one," but "a violet vestment cannot be used on Easter, nor a white one on Pentecost, nor a red one on Christmas."
Another surprise is the following rubric in the 1868 Ceremonial that does seem to go back to Humbert: "Violet may be used in place of black." This odd phrase speaks to a thirteenth-century development underway in Humbert's time. Innocent III forty years earlier had spoken of the liturgical colors as only "white, red, green, and black." But he mentions that violet has come into use in certain places. This Dominican rubric seems to reflect that older practice of using black not only for Requiems, but also on all other penitential days. So the friars had the option of conforming to the local use of violet during Lent, Advent, and Ember Days, where this had happened, but the assumption was they were still using black on those days as Innocent had considered normal. In 1869, of course, this rubric would also have permitted violet in place of black at Requiems–a practice that seems to have existed even in the Roman Rite in some places up to that time. Lest there be any confusion as to what the current Dominican practice was, the Caeremoniale of 1869 explicitly states that since the promulgation of the Cloche Missal these old rubrics completely abrogated and not to be followed. That they had to say this causes me a bit of suspicion. Were some Dominicans still following them? Perhaps the nineteeth-century French yellow chasuble decorating this post belonged to some French Dominicans?
The question of the interchangeability of black and violet brings up the issue of what color the paraments would be at a Requiem Mass if the Blessed Sacrament were reserved on the altar. Here what the Caermoniale of 1869 says and does not say is very interesting. About the tabernacle veil we read the following: "The exterior of the tabernacle is to be decently covered by a canopy (conopaeum). The canopy is to be of cotton, woolen, or hemp cloth, and to be white in color or, better, matching the color of the office of the day." The form of this rubric (which is not in Humbert) suggests to me, at least, that the specification "cotton, wool, or hemp" (gossypio sive lana sive cannabe), instead of "silk" (serica), is quite ancient and that the use of material matching the vestments, which would have been in silk, is later. Notice there is nothing to exclude use of any color of the day, including black. And I was unable to find any rubric to forbid a black conopaeum.
So, as of 1869, there was no formal rule in the Dominican Order against use of black tabernacle veils or black antependia on an altar with a tabernacle. But I suspect this was not the practice because of a related rubric. This involves an altar on which there is on-going Exposition of the Blessed Sacrament. In that case, the altar paraments are all to be white, "even if that does not match the color of the vestments for a Mass being celebrated at it." This, of course, concerns Mass in the Presence of the Sacrament Exposed. Again, however, nothing is said about violet or black when the Sacrament is not exposed. Nevertheless, although the rubrics are silent, the earlier specification that the conopaeum may always be white, and the association of the Blessed Sacrament with white here, suggests that perhaps the practice in 1869 might have been to use a white conopaeum at Masses using black vestments at an altar with a tabernacle. But finding out what was actually done in our priories will require much more work than I am ready to undertake right now.
As it is my understanding that the debate over use of black or violet antependia at altars with tabernacles in the Roman Rite was only resolved in the mid-twentieth century, I am not surprised about the lack of clarity in the 1869 Caeremoniale. In any case, I suspect in the last century at least, many Dominican parishes probably just followed whatever the local Roman practice was. The medieval rubrics for Dominican vestment color options seem to envision this kind of accommodation to local practice. And I can assure you that not doing something the "Roman Way" can generate unpleasant comments from those who attend Dominican Rite Masses and from those who see pictures of them. The pressure on Dominicans to follow the common practice, alien to our traditions as it might be, will always be great.