You did not see the flags closely. They have all of the same 'design' as the regular flag, alternating horizontal stripes, a square in the corner with 50 stars, but the artists used two slightly different colors of while to construct the flag. It made them appear to be bleached white or something.
I can understand that it doesn't seem to be a reasonable description (they are all-white stand-ins for what are usually American flags), but it doesn't seem to be a typo / slip of the pen—or were you making some joke or more subtle commentary that I missed?
