Painting will be very helpful for people with post-traumatic syndrome, or those who are constantly in a stress state. The fact that such activity calms the amygdale, i.e. the area of the brain that is responsible for generating emotions. When you focus on coloring pictures, you give your brain a chance to rest and relax.
"The golden age" of coloring books is believed to be 1960-s, because almost all characters were depicted in them, as well as some products (like Planter Peanuts or Campbell Soup)