"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)
Believe it or not, but the painting will help to improve intellectual skills. It stimulates those brain regions that increase the concentration and attention. It will help solve organizational problems. It seems strange that such activity in general is able somehow to train the skill of time management, but it's true. The fact is that for structuring the information meets the frontal lobe of the brain, and the painting of small and intricate details intensifies its work. The more colors you use, the more complex designs there will be, the brain will work better.