Build your colors gradually, and layer them. Apply a light undertone, and build darker colors slowly on top. Crayons can actually be more difficult to layer with due to the high wax content. Don't confuse them with colored pencils! If you want the "look" colored pencil, just use that instead.
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.