Also have issues reading these plates.
I get they are intended to appear black on white when a bright light (from a camera flash) hits them, but the issue is at night with softer light (i.e. dipped headlights from a following car), they seem to spend a lot of time roughly half way in-between states.
I'm fine to have a black plate option, but lets get rid of the color change bit. Optimize for human reading. It is hardly like black background plates are a new thing for camera's to recognize: