Why does a priest wear vestments of different colors?

The sense of sight plays an important role in Catholic worship; the color of a priest’s vestments help the faithful know that certain celebrations are at hand. Vestment colors are:
Green: The color of vestments used during ordinary time.
Purple or Violet: Used during Advent and Lent (along with white and black, may also be used at Funeral Masses).
White and Gold: Most appropriate for Christmas and Easter
Red: For on feasts of the passion of Jesus and for the Holy Spirit, representing red tongues of fire, in addition to being work for the feasts of martyred saints, who shed their red blood for Christ.
Rose: On the Third Sunday of Advent and the Fourth Sunday of Lent, the color rose may be work as a sign of anticipated joy. If you take the somber color of purple or violet and brighten it with some white, it changes into rose, hence the notion of using this color as a visible sign that Christmas or Easter is soon to come.

From the book, Catholicism for Dummies by Trigilio and Brighenti