The UK government is building over 300 miles of "smart motorways". These sections of road are subject to speed camera enforced variable speed limits - where the hard shoulder is used an additional lane at peak periods.
The cameras are grey rather than highly visible yellow - as per SPECS and GATSO cameras. The new cameras will be deployed on the M1, M4, M5, M6 and M25
There has never been a law that speed cameras must be painted yellow. DfT guidance and rules, rescinded in 2007, meant that most cameras were painted yellow with a view to claiming back the installation and running costs of the same. Since 2007, DfT guidance is that speed cameras in a lit street or highway should (not must) be painted yellow. Outside of these areas, the camera should be covered in a yellow retro-reflective sheet. Failure to follow conspicuity guidance has no bearing on enforcement of speeding offences.