I believe this is how they are supposed to be seen. Apparently, ultraviolet light shows the statues more as they really were.
The Smithsonian online also has an article called “True Colors” with a photo gallery.
http://www.smithsonianmag.com/arts-culture/true-colors.html?c=y&page=1#
http://www.smithsonianmag.com/multimedia/photos/?articleID=19828084&c=y
Here’s an example: