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 in pages that are specific for coloring. I have found a few websites that have pages to color that are downloadable. You can also try a resource store for teachers. These specific pages for coloring are pictures or drawings of a variety of design that you alone enjoy. You can make your own coloring book with these pages. After coloring the designs you can write your own narrative about how you feel. Write how the design itself and the colors you used relieved your stress. You can even write a short story about the design if you like, this is your project and it is for your eyes only.
This will help them to not only recognize different colors but to also learn the names of the different colors. Developing these skills will help in later development too as your child begins to learn to read and write. He or she can then learn how to write the names of all of the different colors. You see learning is progressive and incremental - it happens in stages. Step-by-step as I have described. This is the true beauty of learning...the more that your child puts in, the more they will get out of learning. As their knowledge grows, so will their interest in a range of different subjects.