Here's a bit more:
Given additive blending, there’s no way to darken real pixels even the slightest bit. That means that there’s no way to put virtual shadows on real surfaces. Moreover, if a virtual blue pixel happens to be in front of a real green “pixel,” the resulting pixel will be cyan, but if it’s in front of a real red “pixel,” the resulting pixel will be purple. This means that the range of colors it’s possible to make appear at a given pixel is at the mercy of what that pixel happens to be overlaying in the real world, and will vary as the glasses move.