Good news for jailbreak community, Developers Ahmed Bafkir has release some tweak for Whatsapp app. This tweak is named WADarkMode.
For those not familiar with the application, WADarkMode tweak brings a full dark mode to WhatsApp Messenger program. The Tweak provides a dark manner to the whole app turning distinct UI elements And pages completely dark. The best thing about this tweak is that it May be toggled on and off with a simple tap, right from the in-app WhatsApp settings. Just tap on the Settings button and then tap the dark Mode button from left. You can download the WADarkMode tweak from Cydia where it is readily available for free. It works on iOS 11 and iOS 10 only.