All good questions.
You know one of the flags was inverse, too, right? Black stars on a white background, red and white stripes reversed, all faded back to grey so light it could barely be seen against the white - just like the other flag. So, one flag completely faded in the positive, and one flag completely faded in the negative.
So, not bleach. Not actually faded, either. Rather created that way, and installed with no one seeing anyone do it.
Or changed right on the flagpoles...