Google has started rolling out an update for YouTube that gives the app a partial Material Design makeover. This includes a full height slide-out navigation drawer, circular avatars, a YouTube-logo (red) colored action bar and new animations.
Besides the UI makeover, the only functionality change introduced in the update are additional filters. If you open any channel through the app, the action bar on the top will change its color to match the theme of the channel, giving the app a further polished look and feel.
If you are not a fan of Google’s staged roll out, you can download and sideload the APK manually.
Over the last month or two, Google has updated all its Android apps with Material Design, except for Hangouts.