WhatsApp has made several strides in the past couple years in terms of expanding the feature set of its app on the various platforms it serves, from group video calling to more robust administrator controls and notification shortcuts.
Conspicuously absent on its iOS and Android apps, however, is a dark mode for more comfortable use at night-time (or as a simple matter of preference). Those of you who swear by this feature now have reason to cautiously rejoice; an APK teardown by WABetaInfo has revealed several "secret references" to a dark mode, indicating that it is currently in the works, and might enter its testing phase sometime in the future.
Amusingly, the default theme in the Windows 10 Mobile variant of WhatsApp has, since time immemorial, been dark mode. There's really not much else to go along with over here in terms of what this feature might look like - should it exist, that is -, so it's best to temper one's expectations for now..