Facebook is working on - and testing - a dark mode for its primary app. In launching it, the main Facebook app will join both WhatsApp and Messenger, both owned by Facebook and both already sporting dark looks. 

The news comes via Jane Manchun Wong, who posted her findings online, having uncovered some code with one of the latest Facebook for Android app builds. 

She notes that the app is in early stages of development, and so the dark mode hasn't yet reached every part of the app, but these so-called "rough edges" will be ironed out eventually. 

We don't know exactly when Facebook intends to launch this new dark mode enabled app, but it seems it is definitely in the company's plans to do so. 

Over the past couple of years we've seen a rise in the number of apps and software supporting a fully-fledged dark mode. Even Apple has been getting in on the action, first with MacOS Mojave, and more recently, with iOS 13 beta which both support a system wide dark theme. 

Of course, the latter of those also includes the ability for third party software developers to tap in to that and build in native compatibility into their apps. 

The reasons for its rise are multiple. First, for many users, it's just a refreshing change in how an app looks. Dare we say it looks cooler? Second, for OLED based screens, a completely black full screen app saves a lot of power versus a white version and thirdly, it's easier on the eyes. 

For many users, the dark mode is useful in the evenings, when it's dark. A bright app can often be far too harsh on the eyes, causing strain. 

Facebook hasn't officially confirmed the development yet, but we wouldn't expect it to this early into the development. We're curious to see if this makes it into a final build of the app.