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.
Thanks to colorings the child perceives the world pattern, implements its own color discoveries. If a child paints the picture in unusual colors, you should not abuse him for that; it is his own opinion.