Greyscale Test
Mid-greys are where cheap panels drift: a green or magenta cast in the middle of the sweep means the factory calibration is off, which skews every photo and video you view.
The sweep should be neutral — no green, magenta, or blue tint in the middle greys.
How to use this test
Click Start — the test opens fullscreen over this page (nothing is installed, nothing leaves your browser). A control bar at the bottom of the screen lets you switch colors and exit with one tap — touch screens included; the Esc key and your browser's back button work too. Judge the screen in the lighting the test asks for; judging bleed or uniformity in a bright room defeats the test.
Frequently asked questions
How do I fix a color tint?
Use the monitor OSD color temperature, or the OS-level calibration (Windows: "Calibrate display colors"; macOS: Display Calibrator Assistant).