Japanese seniors trying to stay mentally active, and even middle aged folks just looking for a little peace and quiet have made coloring inside the lines the newest fad in Japan, Mainichi Daily News reports. Now special “Let’s Begin Coloring” pencils which can be used for watercolor while remaining erasable are being introduced to help them.

Coloring has emerged as a simple pastime for retired members of the baby-boom generation, and its popularity has surged with claims that thinking about and separating colors has the effect of a mental workout.

Company officials say that sales of coloring goods have more than doubled compared to the period before the boom.