The P-OLED screen in the Pixel 2 XL looks good but not as good as what you'd expect from an OLED-type display. Here's how to fix that. Believe it or not, a quick settings change will make your phone's display look beautiful!
taimen> cp /system/vendor/build.prop /sdcard/build.prop
taimen> vi /sdcard/build.prop
taimen> mount -o rw,remount /vendor
taimen> cp /sdcard/build.prop /system/vendor/build.prop
Once the phone has booted, you should see an extreme difference in quality. Colors will appear much more vibrant.