Butcher's Blue Dress

What is the origin of the custom, which seems all but universal in England, for butchers to wear a blouse or frock of *blue* colour? Though so common in this country as to form a distinctive mark of the trade, and to be almost a butcher's uniform, it is, I believe, unknown on the continent. Is it a custom which has originate in some supposed utility, or in the official dress of a guild or company, or in some accident of which a historical notice has been preserved?