Facebook adds dark mode that can be enabled through secret Easter Egg

A crescent moon emoji is the key to new-look chats

A car passes by Facebook's corporate headquarters location in Menlo Park, California, on March 21, 2018 (JOSH EDELSON/AFP/Getty Images)

Facebook has finally rolled out a dark mode for Messenger – but it can only be enabled through a secret Easter Egg.

The company has been teasing the launch of a dark mode for months, mentioning it when Messenger received a major overhaul late last year. But it hasn't been possible to actually turn it on.

Now, it can be enabled by just sending one character. It is accessed by sending just a crescent moon emoji in any chat.

Doing so will trigger a host of moons to fall across the screen, as well as enabling the option to turn on the dark mode.

Dark mode turns the background of the screen from white to black. That makes chats less garish to look at and can even save battery on some phones.

"Messenger’s dark mode provides lower brightness while maintaining contrast and vibrancy," Facebook said in its announcement. "Dark mode cuts down the glare from your phone for use in low light situations, so you can use the Messenger features you love no matter when or where you are."

Facebook described the feature as "a hidden, limited-time only experience", suggesting that it will eventually be available to everyone and not just those aware of the trick involving the crescent moon.

The feature is only available to those using the latest versions of the Messenger app on iOS and Android. It will roll out to everyone as normal – with a change in the settings that will do the same job as the crescent moon – in the coming weeks.