Facebook-owned WhatsApp will be getting the Dark Mode soon, it was only a matter of time after the same feature got introduced to Messenger and recently Instagram. According to WABetainfo, those who belong to the Beta testing program on Android have already gotten the Dark Theme update on version 2.20.13.
This only indicates the feature will soon be rolling out officially on WhatsApp. The APK is available for download to Beta participants and Dark Mode can be accessed by going to Settings and navigating to Chats to switch it on.
There are four available options in the Display Setting. First is a Light Theme which uses the regular black text on a white background; the Dark Theme which allows you switch around what you have on the Light Theme; a System default that automatically switches between light and dark depending on the time of the day and finally, a Set by Battery Saver option that changes the theme based on battery settings.

If the feature will be coming to Android soon, iOS users can expect to have it as well.