Red is frequently used as a symbol of guilt, sin and anger, often as connected with blood or sex. A biblical example is found in Isaiah: "Though your sins be as scarlet, they shall be white as snow." Also, The Scarlet Letter, an 1850 American novel by Nathaniel Hawthorne, features a woman in a Puritan New England community who is punished for adultery with ostracism, her sin represented by a red letter 'A' sewn into her clothes. This all comes from a general Hebrew view inherited by Christianity which associates red with the blood of murder, as well as with guilt in general. Often, things will be in red to scare. Another popular example of this is in the phrase "caught red-handed", meaning either caught in an act of crime or caught with the blood of murder still on one's hands.
At one point, red was associated with prostitutes, or now, with brothels (red-light districts). In Roman Catholicism, red represents wrath, one of the Seven Deadly Sins. In Christianity, Satan is usually depicted as coloured red and/or wearing a red costume in both iconography and popular culture. Statistics have shown that red cars are more likely to be involved in accidents. The colour red is associated with lust, passion, love, and beauty as well. The association with love and beauty is possibly related to the use of red roses as a love symbol. Both the Greeks and the Hebrews considered red a symbol of love, as well as sacrifice.Psychological research has shown that men find women who are wearing red more attractive.
Courage and sacrifice
Red is also used as a symbol of courage and sacrifice, as in blood spilt in sacrifice or courage in the face of lethal danger. Examples of this are found in the flags of many nations including the United States, as well as in the novel The Red Badge of Courage, in which a soldier in the American Civil War discovers the meaning of courage. Besides the association with guilt previously mentioned, in Christianity, red represents the colour of Christian martyrs who suffered death for their faith. It is sometimes used for Holy Thursday and during Eastertide, and red green and white is the colour scheme of Christmas. In Roman Catholic tradition it is used for all feast days of Christian martyrs as well as Palm Sunday in anticipation of the death of Jesus. Along the same lines, red is associated in Roman mythology with the god of war, Mars. A Roman general receiving a triumph had his entire body painted red in honour of his achievement. The phrase "red-blooded" describes someone who is audacious, robust, or virile. In English heraldry, red (called gules) denoted ardent affection or love, while crimson (blood-colour) stood for boldness, enthusiasm, or impetuosity.
Green:
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There is an ambivalence in many of these meanings as green is equally associated with death and evil in many cultures. Thus, while green youth, hope and gladness it can also mean change, transitoriness and jealousy(probably why they sing the word "jealous").