This is an Ember day. See here. It is known as the Golden Mass, so called because the first words of the Gospel, which is the Annunciation, were overlaid in Gold.
The Annunciation is of course intimately bound up with the Incarnation and the Feast of Christmas. Well, everything about our salvation is bound up. And as we have contemplated the coming of the last of the Old Testament Prophets, John the Baptist, and now see that the fullness of time has come, and all things are ready, so it is fitting that we contemplate the message of the Incarnation.
When I explain the Immaculate Conception to the boys at school I do so through the moment of the Annunciation. So that she could make a valid choice, not taintend by self-honour or worth, the Blessed Virgin had been preserved from all sin.
So the Gold we celebrate today is the preparation of the world, the preservation of the Virgin and the foreshadowing of the Epiphany.
On a lighter note, I did not dream of mathematics last night... though lots of people did die.