Myths, folklore & symbolism
blue: The color of heaven, distance, and water, it is usually experienced as transparent, pure, immaterial, and cool. In addition, blue is the color of the divine, of truth, and of fidelity (in the sense of clinging to truth, as well as with reference to the fixed firmament of heaven).
Blue is the color of the unreal and fantastic. Occasionally it is used in a negative sense (e.g., in German "to be blue" means to be too drunk to think straight; in American usage "blue" means sad or morose).
Egyptian gods and kings are often depicted with blue beards and wigs. The Hindu divinities Shiva and Krishna are usually shown as blue or bluish-white. Jesus and Yahweh are enthroned above the azure sky.
In Christian painting the battle between heaven and earth was frequently imaged in the opposition of blue and white against red and green (e.g., the battle of St. George and the dragon). As the color of Mary's robe, blue is also a purity symbol. In the Orient, blue is still thought to protect against the evil eye. (Herder)