There is another advantage of colorings for adults. Most of them are very nice and include impressive black-and-white contours that can be turned into a work of art. Imagine the feeling of satisfaction that you get when you have finished drawing and will be able to appreciate the beauty of the masterpiece created by you personally.
There are rare instances of contour drawings of famous architectural structures and monuments with a variety of parts made in a realistic manner. Such coloring is complex to implement and is designed for adults.