Not sure if I've enabled something somewhere or whether it's happened as part of an app update but I am now getting a gradient background when moving through the homescreen which is loosely based on the icon / item I'm over.
For example when I am over YouTube the background is a red-y gradient.
No more plain black!
That's part of the update, if you look for oreo on android tv reviews when it was announced back in june on youtube, they explained that when you are over the apps, the background color changes based on the color of the app.