score:2
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, "Cincture"):
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: "the Sacred Congregation of Rites forbids them [altar boys] to wear a cincture."