Colour Theory

Colour as symbol

		Red through its association with fire and blood is used to represent danger, anger and violence. For the same reason it is also associated with affairs of the heart: love and passion.
		Orange symbolises creativity and endurance. As a secondary color it combines elements of the colors used to mix it. It unites the creative passion of red with the clarity and wisdom of yellow.
		Yellow is the color of the sun - the life support for our planet. As such it has come to represent life, energy, happiness, hope and wisdom.
		Green, as the color of plants and grass, is the color of nature and all that is associated with health and growth. However, it is also used to represent more negative traits such as envy and inexperience.
		Blue is the coolest and most calming of all the colors. As the color of the sky, it has been used since ancient times to represent heaven. In classical mythology, blue was the color associated with the gods, Venus and Jupiter. In Christianity, it becomes the symbol of the Virgin Mary as Queen of Heaven. As the color of the ocean, it is also suggests qualities like freshness, purity and hygiene.
		Purple is the color of royalty, wealth and power. In times past, purple dyes were rare and expensive. Only the rich and powerful could afford to wear clothes of this luxurious color.
		Brown is the color of earth, wood and stone. As such, it evokes craftsmanship and the great outdoors. It is also used to represent humility: a down to earth virtue.
		Black and its association with darkness is used to represent death, evil, witchcraft, fear and sorrow.
		Grey is the natural color of some metals and stone, but it also has negative associations with the weather, boredom and old age.
		White and its association with light is used to represent peace, purity and goodness.

Obviously these are all generalisations, they can depend on different countries and cultures.

Colour as emotion

The Tragedy (1903) by Pablo Picasso

People see emotions in colours, just as they are associated with symbols. This image above Pablo Picasso is increasingly sad and depressing and cold due to the shades of blue that he has used. If this image was in red we would probably read the distance between the subjects in the painting as heated and angry. Colour can change the mood of an image.

(images from this post were sourced from http://www.artyfactory.com/color_theory/color_theory.htm)