Commercial roller mills enable the miller to strip layers off the wheat berry; once the outer layers are removed, milling white flour from the center endosperm is relatively easy. Most home mills use stones or burrs to crush the berries, or a high-speed/high-impact chamber to 'explode' them - that makes it much more difficult to separate the non-white components out of the flour.
That said, I picked up a #50 classifier sieve so I can make fake high-extraction flour from commercial stone-ground whole wheat, in a pinch.