In phrases such as blue-sky talk and blue-sky research, the adjective blue-sky is used to mean:
– in negative sense: fanciful, hypothetical; not applicable, practical or profitable in the current state or situation;
– in positive sense: creative or visionary; unconstrained by current or conventional assumptions, models and applications.

This use of the adjective blue-sky, which seems to have originated in American English, is based on the notion of a blue sky as a place free from disturbances or difficulties.
—Cf. also the phrase blue sky and hot air, first recorded in 1903: this phrase was originally used in the sense of an impractical scheme based on empty talk, the element blue sky denoting an unrealistic project, and hot air denoting insubstantial claims.

 

BLUE-SKY TALK

 

The phrase blue-sky talk (also blue-skies talk) denotes insubstantial or hypothetical claims.

The earliest occurrences that I have found are:

1-: From an advertisement for Swiler Bros. Big Store, Stillwater, Oklahoma, published in The Payne County Populist (Stillwater, Oklahoma) of Thursday 8^th February 1900:

We aim to keep nothing but the Very Best of its kind, and our guarantee is worth more than all the “Blue Sky” talk of peddlers and fakirs that are here today and gone tomorrow.

2-: From an article describing how the Detroit Republicans schemed to catch the Polish vote, published in The Detroit Free Press (Detroit, Michigan) of Thursday 21^st February 1901:

The Republicans base their blue-sky talk of future success on the assumption that they will be able to control the election of city offices next fall, and to do this a plan has been in working order for some time to capture the Polish vote.

 

BLUE-SKY RESEARCH

 

The phrase blue-sky research (also blue-skies research) denotes research that is not directed towards any immediate or definite commercial goal, but may have applications in the distant future.

The earliest occurrences that I have found are:

1-: From the Oregon Daily Journal (Portland, Oregon) of Friday 7^th March 1947:

WHO YOU GONNA HEAR?
Margaret ¹ Makes It Hard for Fans
By Dick Fagan

[…]
The Fagan Research Institute for Things Not Normally, If Ever, Researched did a blue sky research on the horrible situation confronting Charlie McCarthy ² and Fred Allen ³ this Sunday […].
Miss Truman is scheduled to warble with the Detroit symphony from 5 to 6 p. m. Sunday over KEX (ABC), while at the same time in Portland KGW (NBC) airs Charlie McCarthy and Bergen from 5 to 5:30 p. m., and Fred Allen from 5:30 to 6 p. m. During that hour an all-musical show and the Mutual network’s “Special Investigator” also are available on KALE while KOIN carries “The City” and the adventure series “Man Named Jordan.”
Since this is the first time Miss Truman, whose ambitions to become an opera singer have been pretty well publicized, has been on the air before a nation-wide audience, it’s a foregone conclusion everyone—even Senator Taft ⁴—will be mighty curious about how she’s going to do.
Miss Truman’s singing might become the biggest issue in the 1948 presidential campaign, but it’s Charlie and Fred who are in the dilemma this Sunday.

¹ The only child of the Democratic statesman Harry S. Truman (1884–1972), President of the United States from 1945 to 1953, Margaret Truman (1924-2008) was a classical soprano.
² Charlie McCarthy was the dummy of the ventriloquist Edgar Bergen (1903-1978).
³ Fred Allen (1894-1956) was a comedian.
⁴ The Republican politician Robert A. Taft (1889-1953) represented Ohio in the United States Senate from 1939 to 1953.

2-: From The Miami Herald (Miami, Florida) of Wednesday 18^th January 1956:

“State Well Suited”
Wilson Hails Florida’s Bid for New Industries

Fort Lauderdale—Florida’s bid for new industries got a nod of approval Tuesday from Charles E. Wilson, board chairman of W. R. Grace & Co. and former president of General Electric Co.
[…]
W. R. Grace & Co., which operates steamship lines, airlines and chemical companies, has North Florida phosphate expanding its Florida activities at present, Wilson declared.
“I tried 20 years ago to get General Electric to put their ‘blue skies’ research laboratories in Florida. I think the state is well suited for laboratories dealing in pure research because it is isolated from manufacturing centers.”

3-: From The Grand Rapids Press (Grand Rapids, Michigan) of Thursday 6^th March 1958:

Controllers List GE Specialist
William A. Reich, manager of advance engineering, metallurgical products department of General Electric Co., Schenectady, N. Y., will speak on “Blue Sky Research” at the 6 p. m. Wednesday dinner meeting of western Michigan control, Controllers Institute of America, at the Peninsular club.

4-: From Sea Water Conversion Too Costly, published in The Arizona Republic (Phoenix, Arizona) of Friday 18^th April 1958:

Washington (AP)—Several engineers told congress yesterday there is no present prospect of making fresh water out of sea water at a price farmers can afford.
[…]
Fred A. Loebel, vice president of the Cleaver-Brooks Co., Milwaukee, and Edward G. Fochtman, supervisor of chemical engineering research for Armour Research Foundation, Chicago, suggested that the goals of the government program be re-evaluated.
[…]
Loebel said there is a prospect of producing fresh water from the sea at a price some water-short communities can afford to pay. He presented calculations that conversion processes could provide 60 gallons of water per person per day at a cost of $2.15 a month per person.
Fochtman urged that around a million dollars a year be devoted to what he called blue sky research—a search for absolutely new ideas.