TERRE HAUTE, Ind. » Think coloring is just for kids? It’s not really.

This favorite childhood activity has recently become a popular trend among adults, especially members of the millennial generation, those born after 1980. It has been so popular in the U.S. and U.K. that adult coloring books are among the top 10 bestselling books on Amazon.

Local booksellers say that this phenomenon has already found its way to Terre Haute.

Elizabeth Bertucci of Books-A-Million, at 3370 U.S. 41, said bookstore employees started getting questions about adult coloring books in the spring, "but they really took off when summer hit."

"It ended up becoming so major that we now have at least four different spots" in the store to display the coloring books, she said. Now, the store is having a hard time keeping the coloring books on the shelves. "We sell them very often," she told the Tribune-Star.

An avid colorer, Bertucci said the activity is calming and helps pass time or allows her to "zone out."

"It’s something that screams their inner child," she said. She estimated that the bookstore has sold close to 400 adult coloring books since spring.

Another bookstore chain, Barnes & Noble, which also sells adult coloring books, went as far as hosting an adult coloring event on Thursday. Dubbed "Coloring: All Grown Up," it brought together friends and co-workers for two hours of coloring.

"This brings back (childhood) memories," said Terre Haute resident Lauren Cole. The event organizers provided sheets of paper with patterns — and crayons/colored pencils — for the participants to use.

Cole, 26, chose a pattern with the words: "Life is about using the whole box of crayons."

"I honestly like the saying," she said while using different colors for the page. "It’s very true."

To her, the words can be a metaphor for life, which brings "sunny days" (represented by the bright colors) and "gloomy days" (dark colors), and "they all even out."

"You want them to equal a beautiful life," she said.

In addition to remembering her childhood, she believes the activity is a good stress reliever. It’s also a good way to strike up conversations, she added.

Barbie Fox, Barnes &Noble community outreach manager, said she got the idea for the event from a similar out-of-town activity that she has read about in the news.

"Coloring is one of the biggest trends right now for adults all across the country," she said. "They want coloring books, they want something easy, something fun, something inexpensive that they can do to de-stress, to relax, to have fun at home or out with their friends."

"Terre Haute needed an adult coloring event," she said, "and the response has been absolutely overwhelming."

About 80 people signed up for the event, about half of them showed up during the first hour. It was free, but the participants were welcome to purchase a coloring book, drinks and snacks. While coloring, the participants also got to listen to live music.

One adult colorer, 27-year-old Hillary Rains, bought the coloring book, "Enchanted Forest" by Johanna Basford, at the bookstore. She worked on coloring the pages of her new book while enjoying a chat and drinks with her friends.

But the pages that Rains and other colorers worked on were not designs that can be found in children’s coloring books. Rather, these were more intricate and "very detailed," as Rains described it.

Coloring allows for relaxation and creativity, she said. "Keep yourself a kid at heart," she advised. "Just color how you like it."

Her friends agree. "Adults need to play, too," Sarah Freeze put it simply. "It’s good for their mental health."

Several tables down, a group of Terre Haute Parks and Recreation Department employees — and some family members — enjoyed quality time together through the activity. They were all first-timers.

Because "life is so full of everyday trials and tribulations," coloring is a good, healthy activity, said Rita Coleman-Alsop. "I just think it’s fun."

Her daughter-in-law and fellow participant, Pam Decker, said she now has an idea of what to get her mother-in-law for Christmas: an adult coloring book and "a big box of crayons."

"And she will because she won’t forget," Coleman-Alsop said with a smile.