Coloring allows to cope with a variety of emotional problems. For many people, boredom and stress are the main triggers for the emergence of disorders of different nature. This is especially true of people who suffer from anxiety, depression and drug addiction. When patients are engaged in coloring patterns in the book, they concentrate in the picture and keep the focus on the long term. This helps to shift the focus from the negative thoughts to positive and productive mood.
It is believed that the company The McLoughlin Brothers (en.wikipedia.org/wiki/McLoughlin_Brothers) invented the coloring books. They published a book called The Little Folks' Painting Book in collaboration with Kate Greenaway in 1880.