The Chromebook canary channel is getting a Material Design lock screen, as well as a Material Design login screen. This will add a nice little refresh to the visuals for Chrome OS for users even though Material Design is already present in some areas of the operating system. That said, Material Design does not always mean that the visuals will be extremely bright and colorful like you see in many of the Android apps for your smartphones or tablets. With the Chromebook lock screen and login screen, things are much more minimalist than you might expect but it's still Material Design, at least the latest iteration of how these design elements are to be implemented.
Worth noting is that since this is showing up in the canary channel right now, this isn't something that users should expect to see on their Chromebooks natively for a little while. The canary channel is the most experimental version of Chrome OS, just like the Chrome browser, and after this it will still have to make its way through the developer channel and the beta channel before finally transitioning to stable, so it's entirely possible, and also likely, that this won't become a part of Chrome OS for a month or two, or perhaps longer.
Though this is showing up in the canary channel for some, it may not be showing up for everyone. It's noted that it's showing up in build 61.0.3125, though again it's entirely possible that some users on this build of the canary channel might not see the new lock and login screens that feature the material design style that you can see in the screenshots below. With that being the case this may be limited to certain Chromebook models at the moment and if so then Google may be continuing to roll it out to other models in the days and weeks ahead, so if you have a Chromebook, are on the canary channel, and don't see these screens, keep checking as they may pop up at a moment's notice. If you're not on the canary channel and you want to check the screens out for yourself on your own Chromebook, you can switch over to the canary channel fairly quickly, though it's not recommended to be used as a daily build.