Seal your work with Spray Sealer. It is possible to achieve a pebbly look by coloring over something textured. Art stores sell special paper for this purpose. You can also use fabric or other materials. It isn't necessary however to color over texture to create something interesting.
Colored pencil shading is an excellent way to create a great impression.
Price will vary by the size and range of colors, packaging and the quality of the color. Even the little short pencil sets of limited colors give a surprising range of shading possibility. A special feature of Aquarell Colored Pencils is the possibility of creating a watercolor from stamped artwork. You may also use them as standard colored pencils to simply color in impressions. Don't be afraid to add dark colors to shadows or leave some areas as highlights.