A web collection of 1930s prose gives this definition: "A Blue Plate Special is a low-priced daily diner special: a main course with all the fixins, a daily combo, a square for two bits."
The origin and explanation of the phrase are not clear. Kevin Reed says that "during the Depression, a manufacturer started making plates with separate sections for each part of a meal—like a frozen dinner tray—it seems that for whatever reason they were only available in the color blue." Michael Quinion cites a dictionary entry indicating that the blue plates were, more specifically, inexpensive divided plates that were decorated with a "blue willow" or similar blue pattern, such as those popularized by Spode and Wedgwood. One of his correspondents says that the first known use of the term is on an October 22 1892 Fred Harvey Company restaurant menu, and implies that blue-plate specials were regular features at Harvey Houses.
The term became common starting in the late 1920s. A May 27, 1926, advertisement in The New York Times for "The Famous Old Sea Grill Lobster and Chop House" at 141 West 45th Street promises "A La Carte All Hours", "Moderate Prices", and "Blue Plate Specials". A December 2, 1928 article, lamenting the rise in prices that has made it difficult to "dine on a dime", praises an Ann Street establishment where you can still get "a steak-and-lots-of-onion sandwich for a dime and a "big blue-plate special, with meat course and three vegetables, is purchasable for a quarter, just as it has been for the last ten years." The first book publication of Damon Runyon's story, Little Miss Marker, was in a 1934 collection entitled "Damon Runyon's Blue Plate Special". A Hollywood columnist wrote in 1940, "Every time Spencer Tracy enters the Metro commissary, executives and minor geniuses look up from their blue plate specials to look at the actor and marvel."
"No substitutions" was a common policy on blue-plate specials. One 1947 Candid Microphone episode features Allen Funt ordering a blue-plate special and trying to talk the waiter into making various changes, such as replacing the vegetable soup with consommé, while the polite but increasingly annoyed waiter tries in vain to explain to Funt that "no substitutions" means what it says. Our Man in Havana (1958) by Graham Greene has the following exchange regarding an "American blue-plate lunch":
"Surely you know what a blue-plate is, man? They shove the whole meal at you under your nose, already dished up on your plate -roast turkey, cranberry sauce, sausages and carrots and French Fried. I can't bear French fried but there's no pick and choose with a blue-plate." "No pick and choose?" "You eat what you're given. That's democracy, man."
Road food experts Jane and Michael Stern entitled their 2001 guidebook "Blue Plate Specials and Blue Ribbon Chefs: The Heart And Soul Of America's Great Roadside Restaurants".
In contemporary use a "blue-plate special" can be any inexpensive full meal, any daily selection, or merely a whimsical phrasing. A travel columnist says that a Portland, Maine eatery offers "budget blue-plate specials along with more refined fare." The Turner South cable channel calls a daily movie selection, scheduled at lunchtime, its "blue-plate special". Mystery writer Abigail Padgett's second novel about amateur sleuth Blue McCarron is entitled The Last Blue Plate Special; no meals here, the blue plates are part of the decor at a clinic where patients are dying mysteriously. A reviewer uses the headline "The Red, White and Blue Plate Special" for a review of a book on "Diners, Bowling Alleys, and Trailer Parks". There is of course (at least one) blues band named Blue Plate Special. The Boston Children's Museum presents a participatory-theatre show, sponsored by health insurer Blue Cross, which teaches good nutrition; the show is called "Blue Plate Special".