The material. Some coloring books offer the ability for the child to simply run over the surface with the pens or crayons provided, and it will turn out to be the right color regardless. Some are more like paint books, and some have magic marker surfaces and come with markers that will not show up on any surface but the specially prepared book pages. Choose the book that best suits you and your child. If you are worried about markings on the walls, then dont select a pack of basic crayons, get something that uses special crayons. If you want your child to exercise their own creativity and not have to fit in the lines or color schemes planned, get basic pages. It is up to you.
Adult coloring books are all the buzz of late. It is clear that it revolves around colored pencils or crayons and coloring pages. But, it is just coloring, right? How can something like staying within the lines be a benefit to me? I grew up during the time of doodle art - remember those? You got a pack of felt markers and elaborate black line drawings on a number of themes. I would spend hours coloring these in! Little did I know then that coloring pages were a benefit to my well-being.