WhatsApp is one of the applications that will soon also go to the dark theme. We can see it now in beta.
Dark themes are becoming more popular on the mobile. And that's quite natural: to save our eyes in the evening, just like backing up our battery with OLED screens, there's nothing better.
Facebook is making efforts in this direction, and especially on Messenger where it is currently available. His other instant chat app, WhatsApp, will soon join the family.
Dark theme on WhatsApp
The site WABetaInfo has indeed spotted a dark theme was already available on the latest beta released by the Google Play Store. However, the latter is not yet complete, and is visible only on the parameters for the moment.
It does not seem that you can activate it at the moment. This is primarily internal testing by WhatsApp to ensure that the output is working as intended. Patience is in order!
Read on FrAndroid: Dark theme: the best Android apps to preserve your eyes with night mode