The decision means all working cameras on England's motorways and major trunk roads will be yellow by October next year.
Highways England confirmed the plan after ministers ordered a review into speed camera policy this year.
There are about 200 camera sites on England's motorways.
Transport Secretary Patrick McLoughlin said: "I've always been clear that cameras should be visible and get used for safety rather than revenue raising.
"This move is about applying common sense to our roads. Speed cameras should make journeys safer rather than lead to dangerous braking."
Grey cameras were first introduced on the M42 near Birmingham in 2006, following the introduction of variable speed limits.
Highways England chief executive Jim O'Sullivan said: "We use cameras for safety and traffic management only when other more popular solutions, like engineering, are not adequate to tackle particular problems on our network."
The Department for Transport (DfT) said the majority of colour changes will take place during the standard renewal of camera units to minimise costs.
Councils and police forces are required to publish information on the safety impact of speed cameras on local roads.  DfT guidance states these cameras should be yellow.
Grey speed cameras will be turned yellow in a bid to make them more visible and reduce incidents of sudden braking, the government has announced.