Most apps usually have a white background as standard and although this move has its obvious advantages, it also has two main disadvantages which include higher power usage with phones with OLED screens and it is not very friendly to the eyes during complete darkness.
That is why there has been a move to include darker themes on apps so as to rectify these issues people experience with their phones. For example, Google baked in the Day Night theme functionality within Android so that developers could use them in their apps. It seems now Twitter is doing just that which was shown by a screenshot by one Taylor Wimbley on Google+
As you can see, it is just the traditional Twitter for Android app with the dark theme enabled. This is an alpha version of the app (ver 5.112.0-alpha.423) where the guy apparently was not able to turn it off. This means that it is automatic and has a preset where it turns on day and night modes at specific times of the day. Twitter’s dark mode in this case is some sort of navy blue which is rather unique.
That is not all, there is another change with this alpha. There are visual changes to the app like a persistent “compose” button on the bottom right that allows you to post a tweet easily (we’ve seen this on third party apps like Fenix.) Other additions include a hamburger menu where you can access other functions of the app.It will take a while for this to roll out as a stable release and probably by then, more functionality would have been baked in.