OK. I’m just a permanent deacon and a canonist and a former director of deacons. So what would I know?
I see no basis for the conclusion that a permanent deacon has the right to wear clerical attire such as a Roman collar. The code establishes a basis of exception from an otherwise general obligation. This is not the same as an assertion of a right. They are different logical categories.
Unless particular law determines otherwise, canon 288 exempts permanent deacons from the prescription of canon 284 (which people can look up, but also see canon 669 regarding clerical religious).
The current particular law governing the clerical attire of deacons within our episcopal conference is expressed in the
National Directory for the Formation, Ministry, and And Life of Permanent Deacons in the United States, chapter 2, norm 12, which references paragraph 89:
“The Code of Canon Law does not oblige permanent deacons to wear an ecclesiastical garb. Further, because they are more prominent and active in secular professions and society, the United States Conference of Catholic Bishops specifies that permanent deacons should resemble the lay faithful in dress and matters of lifestyle. Each ordinary should, however, determine and promulgate any exceptions to this law, as well as specify the appropriate clerical attire. (89)”
Footnote 97 within the text of paragraph 89, rather than in the norm itself, continues:
“Liturgical books clearly specify the liturgical garb of a deacon for various rites and liturgical celebrations. Here, the intent is to bring about harmony between dioceses, especially on a provincial level, as to the appropriate clerical attire, if any, for other formal clerical ministries of deacons. In some places, deacons wear a clerical shirt and Roman collar; others wear pectoral crosses or deacon lapel pins, while still others wear a modified dress shirt. There is confusion about what is appropriate clerical attire among deacons themselves and among the lay faithful. Recognizing the geographical and social diversity that exists in our country, the Bishops’ Committee on the Diaconate offers this particular law as a practical response to a national concern.”
This suggests to me that the USCCB sees a primary value in the resemblance of deacons with the lay faithful since it mentions that point in text of the norm itself. The expression of intent for the norm, harmony between dioceses, especially on a provincial level, is strangely relegated to a footnote in the source paragraph.
So I would conclude that the emphasis is to be placed on the resemblance mentioned in the norm itself, the footnote notwithstanding. Moreover, as I recall the 1984 Norms of the USCCB on the Permanent Diaconate, it was not envisioned that permanent deacons would normally wear clerical attire.
Having spoken about this issue with three of the former USCCB executive secretaries of the permanent deacons (Sam Taub, Joe Pistone, and Bill Dietwig), I cannot recall any of them in favor of making clerical attire for deacons the common practice
Additionally, as I reflect on my own experience of some 18 years as a deacon, I do not believe that clerical attire was ever once necessary to identify me as a deacon and a Catholic cleric, in any ministerial situation in which I found myself. In fact, when I minister apart from liturgical settings wearing secular clothing or even administer any rites that call for liturgical vesture, I make it a point to identify myself as a deacon. That seems to have been sufficient. It also forfends any impression that I am a priest, and that is a good thing for priests, deacons, and the faithful.
But as the saying goes, what would I know?

By the way, I have made stoles and dalmatics under the tutelage of my gifted wife. I quickly realized the time was better allotted to the functions for which I was ordained.