A few years ago someone from another parish was attending Mass at St. George on a weekday after Pentecost. He commented that it was odd to have me wearing red vestments on a day when there was no martyr's feast. I told him that it was not for a martyr but for the Pentecost Octave. The old calendar of the Church had a full octave of Pentecost (the seven days after a high feast, the feast day itself making eight, and thus "octave"), and so the Monday through the Saturday after were all "solemnities" and thus red like Pentecost. Trinity Sunday is the last day of the eight.
He asked more about it and I pointed out to him that it is the traditional way to observe Pentecost (like Easter and Christmas) and that it helped to keep Pentecost as a higher feast than Christmas (as it originally was). It also meant that the Friday after Pentecost was a solemnity and so the Friday abstinence was dispensed. This is still true for Ordinariate members (sorry, diocesan folks!).
So if you attend Mass at an Ordinariate parish this week (including St. George here in Republic, Missouri) you will see red vestments; not green. You will hear the Gloria recited (or sung) because that is what we do on a solemnity. You will notice that the prayers continue to focus on the truth of the descent of the Holy Ghost. This is because Pentecost is not just another Sunday, it is one of the three primary feasts of the Church calendar.
The story which has made the rounds many times, and I have written about it more than once, is about Paul VI on that first Monday after Pentecost when the octave was dropped. He came in to vest for Mass, and saw green vestments. Asking his assistant where the red vestments were, he was told that the octave was dropped and that it was now green for "ordinary time". "Who decided that?" Paul VI asked; "you did" the assistant said. The Pope (literally) wept.
Beauty and tradition are rich with meaning. They help us to see our Lord better and they enable our spirits to rise to a greater level of holiness. Let us thank God, once again, for the traditions of our faith; and do everything we can to keep them from being lost.