The feast day of John the Evangelist in Catholic and Anglican Christianity. From Wikipedia:

The feast day of Saint John in the Roman Catholic Church, which calls him “Saint John, Apostle and Evangelist”, and in the Anglican Communion and Lutheran Calendars, which call him “John, Apostle and Evangelist”, is on 27 December. In the Tridentine Calendar he was commemorated also on each of the following days up to and including 3 January, the Octave of the 27 December feast. This Octave was abolished by Pope Pius XII in 1955. The traditional liturgical color is white.