When we talk of color, it is the one of the fist thing after noise that attracts a child. A child always tries to catch the color that attracts its attention. Children of every age love colors. It is important to make our children recognize every color, and differentiate between them. These activities are always fun activities that involve education too.
Coloring books for adults is an offspring of art therapy which is a mental health profession that is the process of making and creating artwork which intends to "explore feelings, reconcile emotional conflicts, foster self-awareness, manage behavior and addictions, develop social skills, improve reality orientation, reduce anxiety and increase self-esteem" (according to the American Art Therapy Association). So basically, it's similar to good old therapy. Also, art therapy is not only about mental health and improving yourself - it's a form of personal expression, as well.
It is just a fact of life that kids get bored all of the time. Or at least they believe they are bored. The truth is that these days there is plenty for kids to do. Particularly as computers open up more and more of the world at the click of a mouse. However not much online is suitable for children. And it is always a good idea to get kids involved with activities that require them to be creative.