Some colors are more transparent than others. Some colors are very opaque. Test your colors on a separate piece of paper to see how they work together. Too many layers of crayon can make the colors resist each other. This can make it harder to add more color. Use as few colors as possible to get your end result.
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.