or Azure is the symbol of Divine eternity and human immortality. Consequently, it is a mortuary colour- hence its use in covering the coffins of young persons. When used for the garment of an angel, it signifies faith and fidelity. As the dress of the Virgin, it indicates modesty. In blazonry, it signifies chastity, loyalty, fidelity, and a spotless reputation.
The Covenanters wore blue as their badge, in opposition to the scarlet of royalty. They based their choice on Numb. xv. 38, “Speak unto the children of Israel, and bid them that they make them fringes in the borders of their garments ... and that they put upon the fringe ... a ribband of blue. ”
(See Colours for its symbolisms.)
(A), or a “staunch blue,” descriptive of political opinions, for the most part means a Tory, for in most counties the Conservative colour is blue. (See True Blue .)
“This was a blue demonstration, a gathering of the Conservative clans.” —Holme Lee.
A blue. (See Blue Stocking.) A dark blue. An Oxford man or Harrow boy. A light blue. A Cambridge man or Eton boy. An old blue. One who has pulled in a University boat-race, or taken part in any of their athletic contests.
“There were five old blues playing.” —Standard, May 8th, 1883.
Where I a tub did view, Hung with an apron blue; 'Twas the preacher's, I conjecture.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894