In the early1960s a flurry of coloring books appeared with grown up content. Don't ask me why.
Like children's coloring books, they were printed on cheap pulp paper with simple line drawings suitable for coloring in with crayon. Each page might contain a sentence or two of very simple language, like a child's primer.
The first major example was The JFK Coloring Book illustrated by Mort Drucker. It was intended as a cheap novelty item but it unexpectedly became a smash hit. It sold out multiple printings and spent weeks on the bestseller lists. It was covered widely in the press, including Time Magazine and Newsweek. The Smithsonian Institution bought a copy for its collection.
The JFK Coloring Book was quite profitable for the authors (not so much for the artist). Immediately, numerous imitators stampeded into the market. Artist Jack Davis quickly illustrated a coloring book about Soviet boss Nikita Khruschev:
Drucker was called back for an encore performance with another coloring book about the Kennedy administration.
The same year, artist Shel Silverstein produced the wicked Uncle Shelby's ABZ book, using child-like drawings and language but again, definitely intended for adults.
The glut of coloring books soon saturated the market, and the demand subsided. Illustrators packed up their tents and wandered off looking for the next big thing.
Twenty five years later there were a couple of half- hearted attempts at reviving the market, including the Ollie North Coloring Book and The Ronald Regan Coloring Book, both illustrated by Mort Drucker. The drawings were more sophisticated and the covers were now in color but by this time the moment for such coloring books had passed.
It's difficult to explain the appeal in the '60s of putting adult content in a child-like format. Mark Twain effectively showed the adult world through the eyes of an innocent youth in Huckleberry Finn. In the 1950s, Charles Schulz's strip Peanuts put adult messages in the mouths of small, simply drawn children. Perhaps these coloring books were a continuation of that device. In any event, that fad-- like so many others in the history of illustration-- came and went, leaving some nice pictures behind.