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.
There's also a kind of colored pencils that's called water_coloured pencils. The way of application is just the same as colored pencils. However, with this media you can achieve a watercolor effect by dipping a brush in water and brushing along the colored areas with it. It's actually a fun media to try especially if you want to use a watercolor but find the mixing with water hard. It's easy to use as well.