“What’s red and invisible?”/“No tomatoes.”

A philosophical riddle is:
 
Q: What’s red and invisible?
A: No tomatoes.
 
The joke has been cited in print since at least the late 1980s.
     
     
Google Books
New Society
Volumes 83-84
1988
Pg. 60:
I was told a philosophical joke last week Question: What is red and invisible? Answer: No tomatoes.
 
This may not be very funny but it took on what seemed to me added meaning in the light of a recent attempt to seek out material to cram into the gaping maw of this ever-hungry column.
 
Google Groups: rec.humor
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12/12/90
(...)
What’s red and invisible?
No tomatoes
   
Google Groups: news.groups
ross and dave against the world
sine nomine
12/13/92
(...)
what’s red and invisible?
no tomatoes.
 
Google Groups; alt.locksmithing
Matthew E Cross
4/11/93
(...)
What’s red and invisible?
No tomatoes.
 
Google Groups: rec.humor
Tomatoes
Fai Chan
6/21/93
What’s red and invisible?
No Tomato!!!  HA!HA!HEE!HEE! 
 
Google Groups: alt.tasteless.jokes
What’s red..
Warrick Bell
3/6/94
(...)
What’s red and invisible?
No tomatoes.
 
Google Books
Laugh Out Loud:
A Selection of the Finest Internet Humour, Anecdotes and Wisdom
BY Vivienne Smithdorf and Vanessa Wilson
Sandton, South Africa: Vsquared
2004
Pg. 121:
What is red and invisible? No tomatoes.
 
Twitter
Dr. bess.wiss. Droso
‏@drosophila
*muahaha* Q: What’s red and invisible? A: No tomatoes..
12:46 AM - 9 Sep 2007
 
Twitter
Rich Wright
‏@richwright79
what’s red and not there…? No tomatoes
6:35 AM - 30 Mar 2009
 
Google Books
World’s Worst Jokes
By Tony Husband
New York, NY: Random House
2013
Pg. ?:
What’s red and invisible?
No tomatoes.
 
Google Books
Sensible Nonsense.. Frank’s Comic Pack:
Humour Pack Series
By Frank Paul
BookBaby
2014
Pg. ?:
What’s red and invisible? No tomatoes.