Carolly, A comment for you to ponder about the light. Some sensitive camera are capable to capture history of footprints within seconds because the body gathered the heat to the surface that produces very low light wavelength. When an object that obstacle the sunlight to the surface, it only lessen the light tempature and it cools the surface. The surface still produce some color because of indirect light came from other sources known as Global Illumination. So the shadow are not color property unless your talking about very low light wavelenth from an object; subsurface scatter or converted lights.