When we think of concrete, the color gray generally comes to mind. The traditional mixture of concrete, which comprises cement, gravel, sand, and water may vary in color depending on elements and admixtures but naturally varies from light to dark gray. However, compounds that add pigment to the mixture are becoming increasingly prevalent and popular, as they infuse the concrete with hues more stable than paint. These shades result from the addition of oxides: yellow, red and their derivations (eg. brown) are obtained with the addition of iron oxide; chromium and cobalt oxide create the greens and blues, respectively. For black concrete, it is common to use black iron oxide and carbon oxide combined with pozzolanic cement.