If you have a corner or turn that makes it really awkward not to change direction, you can either color using curved lines or color using very small circles instead of lines. Just keep in mind that how you color will always be visible and will create the appearance of texture.
For a much lighter effect, you can mix a small amount of soft pastel with baby powder and apply it with cotton balls. This technique is usually used for gradient backgrounds. Lastly, enjoy your work! You can keep it in your portfolio folder or hang it on your wall. There are still a lot of ways to use coloring materials in order to give life to your drawings. Just don't be afraid to explore.