Red - Red is the color of passion and sex, not love like it is commonly thought.
Green - Green symbolizes wealth and money, sucess in a career.
Blue - Blue is a calming color, a relaxing color. It helps to improve a mood, and to "drive away the blues", and blue can help assist in mediation.
Pink - Pink is the color of love and friendship.
White - White stands for purity, and is also used for protection.
Black - Black is not a negative color, in fact, black candles are burned to drive away negativity, for protection.
Gray - Gray is a combination of black and white, so it is used for protection.