A new colour scheme for the Desktop app was shared online and developer Mahesh B Wijerathna, who made the discovery, shared his findings on Twitter.
He wrote: "I've been developing the Dark mode for @WhatsApp desktop for sometime now and i just saw these updates on v0.4.930 which has their signature dark color. They might release the dark mode soon. Here's how it looks at the moment. Pinging @WABetaInfo (sic)"
Last month, the social media messaging site explained the Dark Mode feature is "under development" whilst they work out a few kinks.
In a statement, the platform said: "WhatsApp is continuing to work on the Dark Theme, improving the last details before the release.
"It is continuing to add new features for the Dark Theme before the release.
"For this reason, it's normal if you don't see [Dark Theme] in WhatsApp, as it is under development."
The Facebook-owned Instant messaging service made the app's mode to reduce eye strain and reserve battery power available on Android devices such as Samsung and Huawei on the Beta version of WhatsApp last year.
It's also been reported that Dark Mode is heading for iPhone.