This is a really small bug, but the fade-from-orange effect that occurs when you first view a new answer fades to solid white instead of transparent. (This won't be an issue if we remove the background, but if we change it to some other pattern later it might become more noticeable.)
There really isn't an easy way to do this, so we'll just remove the
background-color at the end of the animation.
This won't affect Mathematics now, since it has its own site theme, but it will help on newly created Stack Exchange sites.