This June 17, 2015 photo shows a colored-in page from the adult coloring book “Splendid Cities: Color Your Way to Calm,” by Rosie Goodwin and Alice Chadwick, Hachette Livre (Editions Marabout).

This June 17, 2015 photo shows a colored-in page from the adult coloring book "Splendid Cities: Color Your Way to Calm," by Rosie Goodwin and Alice Chadwick, Hachette Livre (Editions Marabout). It ...

Adult coloring books are giving Harper Lee a run for the money on best-seller lists this summer. Dover Publications has sold more than 3 million adult coloring books with titles like “Flower ...