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.
While coloring pages may seem simple in the minds of parents and other adults these days, they are often the passport into a more creative style of play. Yes, your child will simply color the picture online, but by doing so, she is learning not only to stay inside the lines, but to balance color and texture and to simply use her imagination. If a coloring page for kids is the first step into a full-fledged imagination based entertainment package, it is unlikely many parents will find them simple for long.
You can metaphorically take a page out of a coloring book, and break up the work into a few sections. Each team member or group within the team should first be instructed on which part of the page they are going to color, let them know what color they can use, and when their turn will come up. Next, after each team member has finished their part of the coloring than take the completed picture and hangs it up so that every one can see their part of the picture and the entire teams contribution.