Master of Ceremonies wears purple at High Masses according to the Extraordinary Form of the Mass? Master of Ceremonies wears purple at High Masses according to the Extraordinary Form of the Mass?
I can recall reading in some liturgical book that the Master of Ceremonies (MC) had the privilege of wearing purple (at least the sash) when fulfilling this office at the High Mass in accordance with some norm of rubrics according to the Tridentine Rite. Most MCs would not avail themselves of this privilege. The MC does not have to be a priest, but could be a cleric of lower rank (even a seminarian).
While watching this YouTube video Levithögmässa. 23 november 2019, Göteborg, it is quite apparent that the MC is availing himself of this privilege. It seems equally possible the Master of Ceremonies is a seminarian!
My question is as follows: Can anyone direct me to a reference indicating the use of  a Master of Ceremonies wearing either a purple sash and black soutane or a purple sash and purple soutane?
Once again, I know I have read about it, but I can not recall the source! It may in fact only be a local tradition? I also can recall that the purple sash could be worn.
Was it in a cathedral church?
Nainfa's Costume of Prelates of the Catholic Church (1926) pp. 36-7:

purple is the color of the episcopal Livery. Thus, according to rules laid down by the Ceremonials,4 the Master of Ceremonies of the cathedral church, the train-bearer of the Bishop,1 the cross-bearer of the Metropolitan,2 all the members of the diocesan Seminary, as well as the employees of the cathedral, namely, sacristans, ushers, chanters, etc., all should wear purple cassocks.4. Cær. Episc. I., V., 4. S. R. C, February 29, 1868. — Dec. 14, 1894.1 LEVAVASSEUR-HÆGY, Fonctions Pontificates, II., p. 273. S. R. C., Aug. 2, 1608. Jan. 24, 1660.2. LEVAVASSEUR-HÆGY, Fonctions Pontificates, II., p. 305.


cf. ibid. p. 58 (ch. 4, &quot;Cincture&quot;):

At ordinary times, Bishops and the Prelates di mantelletta are entitled to wear a purple cincture of plain silk over the choir cassock, the ordinary black cassock and the simar. When they wear mourning (black cassock with purple trimmings), they put on a cincture of plain black silk with fringes or tufts of the same color.1 The cincture of the Prelates di mantellone is of no other color than purple.BARBIER de MONTAULT, op. cit., Tom. I., p. 285.

And ibid. p. 60: &quot;the Sacred Congregation of Rites forbids them [altar boys] to wear a cincture.&quot;