Here's something I think might help you a lot with coloring. My highschool art teacher taught me this and it made a huge difference in my work. Every color, is not made up of just one color but usually 3, 5 or even 10 different colors. Make use of complementary colors, triads, and similar tones. Also be sure to keep you pencil strokes very light at first, you can always add more but colored pencil is a bitch to erase. Keep in mind where your lights and darks are and apply strokes accordingly. it can help to have a preconcieved light source. I almost always put mine in the upper left corner.