Google Photos is a fantastic app, but storing and accessing to all your images from the cloud can be a strain on your smartphone's bandwidth and storage, especially if it's a budget Android device. Last month, Google launched Gallery Go (along the lines of Maps Go and Google Go), a lightweight picture manager targetted at the hundreds of millions of budget devices being used in developing countries. Today, the app got an update that adds dark mode — something other apps like Messenger and Google Photos already have.
— Google Photos (@googlephotos) August 14, 2019
If you were running Android Pie (or OxygenOS), you could already enable system-wide dark mode, so today's update won't really enable any new functionality for you, but those running Oreo and older can now enjoy a dark theme too.
Even if you don't have a budget phone it may be worth downloading Gallery Go for when you just need a quick and light app to browse your images with — a sort of Quickpic-replacement, if you may.
The update to v.126.96.36.1992023587 of Gallery Go should be available on the Play Store in the coming days, but if you don't have the patience to wait for that, you could always grab the installer over at APKMirror.