Although fun to work with, coloring pages should not be used often with the preschool grades. Most importantly, children should be allowed to express themselves freely even if using a coloring page. The goal is not to color within the lines, choose colors that are "correct" or even to follow the image in the coloring page at all. Quite often children will be inspired by whatever they see on the coloring page and it will send them on their own creative path. Never judge a child's coloring abilities ... the name of the game is fun and play for learning ...not to "fill in the color blanks".
Several Coloring Pages can be found HERE. More are added regularly.