In Catholic religious art the color blue, not white, is symbolic of purity. The white wedding gown originated in the nineteenth century in imitation of Queen Victoria who wore white for her wedding to Prince Albert. The blue that brides were instructed to wear “something borrowed, something blue” on the wedding day was in honor of the Blessed Virgin Mary, who is so often pictured with a blue mantle signifying her virginal purity. The French, even though they have long forgotten why, honor Our Lady in their familiar exclamation, Sacré Bleu, which traditionally was a plea for protection under her blue mantle.
by Brian Kelly