Black is symbolic of death, and is therefore the liturgical color for Good Friday. Black can also represent sin, which results in death.
Blue, the color of the sky, is symbolic of heaven. It may also be used to symbolize truth. Blue is gaining acceptance as a liturgical color for Advent.
Brown is the color of spiritual death and degradation.
Gray is the color of ash, so is sometimes used to represent repentance and may be used during Lent.
Green is the color of plant life, abundant in spring. It is used to represent the triumph of life over death. Green is the liturgical color for the Trinity season in some traditions, and may be used during Epiphany in others.
Purple is the color for penitence and mourning. It is also the color of royalty. Purple is the liturgical color for the seasons of Advent and Lent.
Red is the color of blood and therefore is the liturgical color for the commemoration of martyred saints. Red is used as the liturgical color for Pentecost, since it is the color of fire (e.g. above, right).
White is a symbol of purity, innocence and holiness. It is the liturgical color for the Christmas and Easter seasons. White is sometimes represented by silver.