WhatsApp updated the design of the Android version of its app to Material Design but it was limited to the APK downloaded from their website, while the Play Store version was still rocking the old Holo UI from the yesteryears.
After a month of releasing the Material Design update on the site, the Play Store version has finally caught up. If you choose to stick to the Play Store version (even though the ones from the website are perfectly stable for daily use) then you should update immediately.
We’ve already gone through the design changes and there’s nothing new in the Play Store version. The design only loosely adheres to the Material Design guidelines so MD purists will likely scoff at it but it still looks a hell of a lot better than the previous Holo design, and is just nicer overall. Check it out at the link below.