WhatsApp included Splash Screen in its Beta Update
WhatsApp's latest Android beta update v 2.19.297 included the splash screen feature for the users. When you open the app a light-colored Splash Screen with WhatsApp logo will show up. According to the beta update also suggests that a Dark Splash Screen is also under development.
Splash Screen is essentially a new page that shows up initially when the app loads for the first time, with the WhatsApp logo plastered on a white background. This new launch screen feature has been spotted on the latest Android Beta update. There might be the chances of getting a dark splash screen feature too.
You can get the beta updates by enlisting or signing up yourself for the beta access program on Google Play Store or download it from an outside source.
Check it out on Google Play Store - WhatsApp
According to WABetaInfo, “Some users might get the Dark Splash Screen, even if the Dark Theme is not enabled. It's a bug that also makes the bubbles dark, sometimes.” Dark Mode hasn't been made available yet, and there's no release timeframe known for it either. However, it has been spotted to be under development in varied beta releases.