The base color for Spiderman was black.
This was followed by the solid layers of color you see, then dry brushed one layer at a time. The black in the crevices on the wall were done with a thinned acrylic brushed on then immediately wiped off with a paper towel. Some real sand was glued to the base followed by real newspapers and pieces of cellophane in the trash can. Painted with mixes of brown, rust and yellow.