Gizmodo describes the state of the flags American astronauts left on the Moon:
While the $5.50 nylon flags are still waving on the windless orb, they are not flags of the United States of America anymore. All Moon and material experts have no doubt about it: the flags are now completely white. If you leave a flag on Earth for 43 years, it would be almost completely faded. On the Moon, with no atmospheric protection whatsoever, that process happens a lot faster. The stars and stripes disappeared from our Moon flags quite some time ago.