Hypsometric

source: http://www.earthexplorer.com/2009-03/subsurface_geology_challenges_goiania_metro.asp

Hypsometric maps use color to depict relief/elevations. The map above has a gradient of color ranging from dark blue (below sea level) to white (highest point above sea level). As you can see, the combination of colors are very effective in demonstrating relief on a 2D image.