Washington Monument. We did not depart the guided bus to go see this but took photos as we drove slowly by it. They told us that the reason what the marble has 2 different shades (at about the lower 1/3 point), is that they stopped construction on it for 25 years and when it started back, the quarry they originally got the stone from had been removing stone during those 25 years so were to a deeper level, hence the difference in color.