Black Screen - Turn any display into a fullscreen color

I built Black Screen around a very simple idea: common display tasks should not require installing another app. The site lets you instantly open clean fullscreen black and solid-color screens in a browser. Typical uses include checking dead or stuck pixels, inspecting monitor uniformity and backlight bleed, reducing unwanted light from a secondary display, testing OLED screens and creating a distraction-free display. I wanted the experience to be as simple as possible: open the site, choose the screen you need and use it. I'd be interested to hear which display-testing or fullscreen tools would make it more useful.