Borrowed from;
Freemasons - About Freemasons;
According to Coil's Masonic Encyclopedia, there may be a number of reasons why symbolic lodges are called Blue Lodges. Since ancient times, the color blue has been associated with immortality, eternity, and fidelity. References to the color blue in the Bible emphasize the special place blue has as a color symbolizing goodness and immortality. The Druids also honored the color while the ancient Egyptians used the color to represent Amun, one of their most important gods. The ancient Babylonians associated the color blue with the gods. In Medieval times, Christians saw blue as the symbol of perfection and hope, and well as of immortality and fidelity.
According to Coil's Masonic Encyclopedia, it is not known when blue first came to be associated with Freemasonry, although some historians think that initially the color was used in Craft Masonry to represent the sky. Today, blue for Masons symbolizes brotherhood and symbolizes the fact that Masons should seek out virtues as extensive as the blue dome of heaven.