If you want a clean and bold look for your picture, you can use colored markers for the color. It has a wide variety of colors and you can choose between fine tipped ones and broad tips depending on your needs. There are also refillable markers where you can just purchase ink whenever it dries up or loses its color. It's also an easy material to use. You just have to apply a single coat on the drawing. You can also add some more details using either a white colored pencil or a white inked pen.
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.