The trend behind the book is fascinating. According to the New York Post, experts started seeing reviews popping up online. In the reviews, people would say they bought a book for a relative but then purchased one for themselves.

This led to a whole new revolution -- the birth of the best-selling adult coloring book. The New York Post reports that France was the first country to be taken by the trend, where Secret Garden sold a million copies. Then China jumped into the mix, where the book sold 3 million copies. Brazil, too, fell in love with Secret Garden to the point that there weren’t enough colored pencils to go around. 

But what about here at home? Did we buy Secret Garden too? In the United States, the book sold 1.5 million copies at the time of the article’s publication. Its follow-up, Enchanted Forest, sold 1.2 million copies. 

Are You a Colorist?

There’s even a name for people who engage in coloring activities. Those who color call themselves “colorists.” They display works of art online and even receive reviews for their pieces. It's a world of its own that may be around for years -- like knitting.

“It’s kind of a way of being creative without the stress of too much creativity. You’re not stressing yourself out as much as you would if you were to draw from scratch, but you’re still getting some of the relaxing qualities of creating,” Peter Gray, professor of psychology at Boston College, tells the New York Post.

However, there may be a bit of psychological reasoning behind this trend too. Author Jordan Gaines Lewis writes about the concept in The New York Times, saying that adult coloring books can make you feel artsy, which spruces up life in general. This may allow people to tap into creativity.