Coloring Books for Adults Are Good for Creativity, and Selling in the Millions Three of Amazon's top 10 best-selling products of 2015 were coloring books.

Adele's chart-topping tunes weren't the only form of therapy adults welcomed into their homes last holiday season. With millions of copies sold on Amazon alone, it seems folks gladly took a break from their ball-point pens and to-do lists for a set of colored pencils and an "age-appropriate" coloring book.

For instance, Jason Abrams, a New York-based PR account manager, took to coloring books and crayons at 22 to offset the anxiety and stress of college life. With his career in full swing eight years later, he doesn't plan on stopping anytime soon.

"Being in a creative field, it allows me to enhance my creativity and think outside the box," he says.

Related: Crayola Launches a Line of Coloring Books for Adults

Abrams says he prefers what's considered "kid" coloring books, with themes ranging from Marvel's The Avengers, football, Star Wars and indie rock. Once completed, he'll keep them, share a picture online or even give it to someone. In some instances, Abrams has used the activity as a fun motivational tool in professional settings.

"It's something I've done for a long time, and what's really funny is that over the years my friends and my family, they kind of laughed about it -- the same reaction I had when I was introduced to it," Abrams says. "But don't mock it until you try it … I'm happy to see the trend is catching on because I do really believe in the power of coloring and I hope it's not a fad that'll go away, because it can do a lot in terms of improving quality of life."

Research supports Abrams. According to an article published by the American Journal of Play, the use of adult coloring books (or play in general) can improve career and academic success, reduce stress and encourage an innovative work performance. The practice can also help train the mind to better focus, relax and reset.

Also approving of the trend and its benefits, The American Art Therapy Association said "since engaging in any form of art can have stress-reducing value, it is no wonder that these sophisticated templates for adult coloring have taken on such great popularity."

These coloring books aren't just some passing activity for people who want to tap into their creativity -- they're big business. Three of Amazon's top 10 best-selling products of 2015 were coloring books.

The most popular to date is Scottish illustrator Johanna Basford's book, Secret Garden: An Inky Treasure Hunt and Coloring Book, having sold roughly 2 million copies worldwide.

Illustrator Jenean Morrison's work also made an appearance on Amazon's Bestseller list. Inspired after discovering an old coloring book from the '70s in 2012, Morrison has since independently created and sold eight titles on CreateSpace, including Flower Designs Coloring Book, which was on the bestseller list for eight weeks.

Selling the books for about $12 each, Morrison earns approximately $5.05 per sale. Overall, she made about $350,000 in royalties from the site in 2015 and has published international editions of her books in eight countries. Morrison is also working with a publishing company to start distributing her work to 50,000 newsstands across the country within the upcoming year.

"Self-publishing is a great way to go," Morrison says. "A lot of publishers right now are looking for coloring books, so it's a viable option."

Though the artist didn't originally refer to her work as specifically for adults until the trend gained traction within the past two years, Morrison recognizes how adult versions are different from more elementary editions because of their complex and intricate designs. They also serve a different purpose, providing a host of potential benefits such as improved mental health or logic, problem-solving and motor skills; something morrison's customers can easily attest to.

"This book will inspire your imagination, stimulate your senses and creativity, and as you become engaged in the enjoyable activity of Coloring, it calms you and almost immediately starts reducing your stress level," Jackie Cooper wrote, an Amazon user and reviewer of Morrison's best-selling book.

Related: Business Idea Center, Coloring Books