You have a greater tool - your PC - that can be helpful to get the printouts of diverse colorful sheets. Guide the children, exclusively during the holidays to add illustrations to the colorful-page, and showcase them around the prominent places of the house. This will give them, a sense of pride and joy for their creativity, and would lead to further productive pursuits. Thus, you will witness that there are massive advantages of coloring-page relatively to coloring books. Coloring sheet are economical, costing you only a couple of cents in ink and paper rather than a few dollars for a coloring book.
Coloring is a great way to bond. Ask your friends over for some wine, cheese and coloring. Perhaps at first they might look at you with skeptical eyes and doubt; but hand over a fresh sheet of paper, some vibrant or glitter colored pens and in just minutes you will not be able to pry those colors out of their fingers. Soon you will be visiting easily, looking over at each-others masterpieces from time to time to admire their selection of colors. You will begin to feel like you have time-traveled back into grade 2 and you do not really want to leave. Coloring is freeing and has no expectations. The beautiful thing about this craft is that there is no pressure to finish, to use a certain color or even to stay in the lines!!! There is absolute freedom involved in those precious hours where you just get to color.