The Road Vehicles (Display of Registration Marks) Regulations 2001

ARequirements where the vehicle carries a registration plate which is constructed so that the mark may be illuminated from behind by virtue of the translucency of its characters.

1.  The registration mark must be formed of white translucent characters on a black background on the surface of that plate.

2.  When the registration mark is illuminated during the hours of darkness, the characters on that plate must appear white against a black background.