Other contributors have said "What color is the Abe licoln monument?" is the same question as "Why does the Washington monument change color?" If you believe that these are not asking the same thing and should be answered differently, click here
The Washington Monument changes color because of the different types of building material used. Construction of the monument was stopped for about 20 years. When contruction resumed, a different shade of mable/granite was used.
The color changed on the Washington Monument because it was built during two different periods with two different type of stones. One third of the building was built when Congress had to stop for the...