The Calendar prescribes different degrees of celebration, the following list is in order of importance:
Solemnities
On solemnities the Gloria and Creed are used at the Mass. The Mass propers and readings are set especially for the day.
ie: The Epiphany(6th January), The Assumption of the Blessed Virgin Mary(15th August)
Feasts
On feasts the Gloria is used. The Mass propers and readings are set especially for the day.
ie: Apostles, The Presentation of Christ in the Temple (Candlemass)(2nd February)
Memorias
On memorias the Gloria is not used. The mass propers are of the day, but the readings used are often for the normal weekday.
ie: Charles, King and Martyr, 1649(30th January),
Other Commemorations
On commemorations of holy men and women who have not been formally canonized but who will be remembered. The normal weekday propers and readings are used.
ie: William Laud, Archbishop of Canterbury,1645(10th January)
Feria
Feria refers to a day on the Liturgical calendar on which no feast is observed.
White is the colour of purity and innocence and is worn on the feast days of Our Lord, the Holy Virgin Mary, the angels and the saints who are not martyrs.
Red symbolises fire and blood, and is the colour of martyrdom, the Holy Ghost, the Crucifix and the apostles. Although never worn for extended periods, the colour red is seen throughout the year, and denotes individual feast days.
Green represents life. It is present on ordinary Sundays, and after Epiphany and Pentecost.
Purple is the symbol of quietness and penitence. Violet is worn on the Sundays and weekdays of Advent, during Lent, on feast days at the beginning of each season, before a period of fasting and on pilgrimages.
Black is the colour of mourning worn on Good Friday, on All Souls Day and at masses for the dead.
Pink marks the pauses for joy during periods of penitence and fasting.
Gold is permitted on holidays and can replace white, red and green but never black.