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.

Aldershot nearly led before the break when Rhys Browne set up Lafayette but Marek Rodak saved and Charlie Walker failed to score on the rebound.
The visitors kept pressuring as Jake Gallagher and Jim Stevenson forced Rodak into further saves.
Victory for the Shots was sealed when Rodak brought down Lafayette and he scored from the spot on 76 minutes.
Aldershot Town boss Barry Smith told BBC Surrey:
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"You know it was a very scrappy game and Welling gave us a lot of problems in the first-half.
"I thought at half time we upped our levels and we caused them problems in the second half and I think we deserved to win the game.
"I've got confidence in the strikers and confidence in players who can score and it was a matter of time. Their keeper made some terrific saves, but you've got to keep believing like we've done this season."
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.
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Ross Lafayette scored a second-half penalty to seal all three points for Aldershot Town as they beat Welling.