The new colour adjustment app includes 15-20 much better images (many of them are what we use internally). It includes images to check near-white, near-black, red green blue channels, clarity, full dynamic range etc etc. Also included are common test patterns.
This app will be available to beta testers shortly, and to everyone else in the next SW update.
Also the systems team is checking what options we have to show the UI on top of whatever is being displayed. (Though since external inputs are bypassing the android layer, the UI will only overlay on top of internally playing content).