The finished appearance of concrete comes from the combination of materials used to make it. Concrete is composed of aggregates—sand and small stones of varying sizes, cement, and coloring agents (pigments) mixed with water. Many color and texture options are possible by varying aggregate color, size, pigments, cement color, finishing processes and depth of exposure.
Cement, pozzolans, and sand are blended to form a matrix which surrounds the stone. This matrix can be colored—either using colored sand or powdered pigments or both—to match or contrast with the stone.
Cement can be gray or white. Gray cements usually cost less, but require pigments to assure color consistency. White cement is used where light or highly consistent color is required. Sometimes waste-byproduct pozzolans—in concrete terms, a powdered material that improves the strength or other properties of the concrete—such as fly ash, silica fume, and slag are used to reduce the cement used in a mix.