You can add texture to a watercolor painting by using the dry brush technique. This works with cold pressed and rough watercolor paper. Hot pressed watercolor paper is perfectly flat and ironed out. This can be done with any color of watercolor and it does not matter if it is a transparent or opaque color. The trick to behind the dry brush technique is in the amount of water to paint ratio. No you are not using a totally dry brush, you never want to paint with a totally dry brush, always wet your brush before dipping it into watercolor paint.
You want to use less water and more paint. Dampen your brush and blot some of the water out, pick up some color and lightly drag the side of your brush across the top surface of your paper. The bumps and dips in the paper will help create the textured look. It can be done with either a round or flat brush. Practice a bit and give it a try.
Dry brush is great for creating texture in landscapes.