Holy Days

The Catechism of the Catholic Church explains holy days of obligation this way:

On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord's Day, the performance of the works of mercy, and the appropriate relaxation of mind and body.

Family needs or important social service can legitimately excuse from the obligation of Sunday rest.

The faithful should see to it that legitimate excuses do not lead to habits prejudicial to religion, family life, and health [CCC 2185].

light innocence purity joy triumph glory	White   Season of Christmas Season of Easter Feasts of the Lord, other than of His passion Feasts of Mary, the angels, and saints who were not martyrs All Saints (1 November) Feasts of the Apostles Nuptial Masses Masses for the dead (Requiem Masses) when the deceased is a baptized child who died before the age of reason Note: White is the color of Popes' non-liturgical dress. White can be replaced by Silver.
the Passion blood fire God's Love martyrdom	Red   Feasts of the Lord's passion, Blood, and Cross Feasts of the martyrs Palm Sunday Pentecost Note: Red is the color of Cardinals' non-liturgical dress
the Holy Ghost life eternal hope	Green   Time After Epiphany Time After Pentecost
penance humility melancholy	Violet   Season of Advent Season of Septuagesima Season of Lent Rogation Days Ember Days (except for Pentecost Ember Days) Vigils except for Ascension and Pentecost Good Friday Note: Violet, literally "amaranth red," is the color of Bishops', Archbishops', and Patriarchs' non-liturgical dress
mourning sorrow	Black   All Souls Day Masses for the dead (Requiem Masses), except for baptized children who've died before the age of reason
joy	Rose   Gaudete Sunday (Third Sunday of Advent) Laetare Sunday (Fourth Sunday of Lent)
joy	Gold     Gold can replace white, red, or green (but not violet or black)