A small child's intellectual capabilities begin to develop as soon it is born and by age 4 they have developed most of the basic capabilities they would require for their adulthood. The brain never stops growing though and keeps on assimilating and organizing the knowledge it had acquired.
To expand those intellectual capabilities and help the brain grow coloring pages are a very good form of intellectual exercise.
These coloring pages range from Disney characters to religious festivals. There are coloring pages available online on every conceivable topic you can think of. The primary stimulation to the brain they provide is that knowledge of colors. It is not merely colors that help but the kids get that aesthetic sense by the act of coloring. He starts to recognize the various shapes and forms. He also gets to know what are boundaries and lines.
As a young ones parent or a school teacher you need to plan activities with him for coloring pages. For the most part the parents tend to give those coloring pages to kid to keep him busy. But the fact is that these kids need to get some mental exercise from these coloring pages and it should be construed by the kid as a mundane exercise.
Of course it takes a little bit of creativity to get the coloring page activity to be fun. For example if there is a festival just round the corner then get your kid all the coloring pages related to the festival. That way he or she can lean about all the festivals. Make sure to make this fun and interesting by inviting other friends of his age group to your home and have a nice contest among them. Better still tell them to create images of the festival activities and let them exchanges those drawing sheets with each other for coloring.
That said make sure that the kid prints those coloring pages on a used sheet of paper and tell the kid not to waste paper. That way you will also make sure that he grows onto to become and environmentally conscious individual.
The author has a resource on Disney coloring pages characters and he advocates the use of Disney coloring pages to stimulate the kids brain intellectually.