In the United Kingdom, the backs of road signs are normally painted grey.
The grey back is a practical convention rather than a message to drivers. It gives signs a consistent appearance from behind and helps distinguish the rear of a sign from its face, which uses colors and symbols to communicate road information. Sign supports and mounting arrangements can vary, but the standard rear finish is generally grey.
Drivers mainly see the front of signs, where color carries important meaning. Blue is commonly associated with information or motorway routes, green with primary routes, and white with many regulatory or local-direction signs. Warning signs generally use triangular designs with red borders, while regulatory prohibitions commonly use red circles.
The rear of a sign should not be mistaken for a sign face viewed from the wrong direction. It normally provides no instruction to approaching traffic. Exceptions can occur for temporary works, special installations, or local design details, so the grey convention is best understood as the normal national standard rather than an absolute rule for every object by the roadside.