Today there is a large set of coloring books. You can find coloring-cursive books, books outliners, for boys (all sorts of appliances, machines, robots, etc.), for girls (fairy-tale characters, dolls, funny funny little animals). There's even a wallpaper coloring books that opens a wide field to have enough space for young artist.
Coloring also takes us back to a time when everything was easier. You agree that such activity would seem more suitable for kids than for adults. In fact, painting is associated by most people with the period when they did not have much to do, and carelessness was more than enough. In order to take a little dip into childhood and clear the emotional background, coloring is an ideal option. It seems to take us out of the current stress state and allows forgetting about everything for a few hours.