Google has started rolling out the Gmail 5.0 version which includes many new features. One of the features is the expected Material Design UI. Another great feature is the support for other accounts like Yahoo, iCloud Mail, Outlook and basically any account that supports IMAP/POP or Exchange.
Gmail is now another app where you can have all the accounts at one place so there is no need of the stock email app now. However the Inbox option will show the messages of that particular account so you will need to switch to other account in order to see the messages of that account.
Material Design is another update in the new version. There is a redesigned navigation drawer, which looks sharper and has a new interface for switching accounts that works better (and is faster) than before.
And also the Email contact picture is now changed to a round icon rather than a square one and there is a red color instead of the grey one.
If you have not installed the new Gmail app till now, grab the APK from here and install it using any file explorer.