Blue-plate special

What exactly is a "Blue Plate Special?"
thanks for any input
Linda

Originally the featured meal of the day, offered at a bargain price, in inexpensive restaurants such as diners. My sources don't say when blue-plate specials were popular; I'd guess early 20th century.
Definition of "blue plate" in Webster's Unabridged, 1934: "A plate with a blue design; esp., one divided into compartments, for serving several kinds of food, as meat and vegetables, as a single order."