Brighter results! Applying less pressure to the pencil will produce a lighter color, so how do you get that darker hue of the color on the page without pushing too hard? The answer is layers. Once you have mastered coloring between the lines with a nice even shade, you can take the same pencil and go back over that coloring again to provide a second or even third layer of color. Applying extra layers of color will remove some of the white grain that was missed in the first layer and bring depth to your color. Mix up the direction you color each layer to produce a smoother finish.
Consistent Pressure Gives a Uniform Look. Keeping a consistent pressure with the crayon on the paper gives a uniform, pleasing look. If you're pressing hard, your hands will get tired quickly, so I prefer to press lightly. Interestingly, being aware of how much pressure you're applying seems to be really hard for younger children. It must be tied to motor skills in some way. It won't hurt anything to tell them this tip, but if they aren't implementing it, just let it go.