Many new coloring book titles are being marketed to stressed-out, work-addled adults, who benefit from the quiet zen that a coloring session can bring.

Coloring books for adults — a genre once considered little more than a novelty — are suddenly a big business, a bright spot in the financial results of publishers and retailers alike.

In 2014, 1 million coloring books were sold; in 2015, 12 million were sold. The coloring book craze even drove an echo boom in coloring pencils, with sales increasing by 26.4 percent in 2015 from ...