The setting, dubbed dark mode, converts icons, menus and backgrounds to darker colours in a bid to dampen the blinding effect they can have when viewed in pitch black conditions.
The tool is also better for battery life as it cuts the brightness used by the smartphone to power the display.
A slew of popular smartphone apps, including YouTube, Microsoft Outlook and Twitter, have already introduced the feature.
Dark mode, which has already surfaced in the early beta test versions of the next WhatsApp update, is expected to roll-out to users worldwide very soon.
Like the dark mode already in use by other smartphone apps, the tool aims to cut the amount of blue light that reaches your eyes.
Blue light can disrupt your sleep patterns by meddling with the body's internal clock, and scientists recommend limiting your exposure to it late at night.
Dark modes, sometimes known as night mode or dark theme, typically flip the switch on an app's default colour scheme to achieve this goal.
WhatsApp's plans for a dark mode were sniffed out by technology blog WABetaInfo.
The publication regularly combs through WhatsApp's beta code to uncover new features and has a solid track record for leaking upcoming WhatsApp features.
In a post to Twitter, the site said: 'I'm happy to exclusively give the good news: WhatsApp is finally working on a Dark Mode! It's a dream.
'There are many important secret references in recent updates.'
As well as sleep benefits, dark mode also helps your battery last longer.
For those with devices that use OLED screen technology, blacks displayed on the screen will not activate individual pixels – meaning much less power is required.
While dark mode is currently included in the latest beta, this is no guarantee the messaging service will decide to roll-out the tool to its users worldwide.
WhatsApp regularly tests new features that do not make it into the final version of the app update.
WhatsApp was not immediately available for comment.
