There's a lot to like about the new Pixel phones—they're fast, the battery life is improved, and Google fixed the Bluetooth. You also get a lot of thoughtful software features that aren't available on other phones. For example, the launcher theme changes automatically based on your wallpaper.
This actually confused me quite a bit when I first started using the Pixel 2 because the light theme to which I've become accustomed just changed suddenly. I didn't realize at first it coincided with changing my wallpaper. If you choose an image with lighter colors, you get the predominantly white theme. If you pick something that's mostly dark, the launcher toggles the dark theme on. You do have to go pretty dark to trigger this, though.
The traditional light theme.
The dark theme affects the app drawer, folders, and quick settings. The quick settings aren't technically part of the launcher, but that's okay. The dark theme looks great there. I wish I could just turn on the dark quick settings manually. Maybe Google will include a few options like that in future updates.