Coloring in for adults is actually surfacing as a popular app niche too - https://play.google.com/store/search?q=coloring%20books%20for%20adults https://play.go

Coloring in for adults is actually surfacing as a popular app niche too - https://play.google.com/store/search?q=coloring%20books%20for%20adults https://play.google.com/store/search?q=coloring%20books%20fo...