E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
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.