Many laptops, even some of the higher-end business models, can still show clouding or light leakage on dark backgrounds. This can depend on the panel supplier or just normal variation between units.
When I was testing a few devices recently, I found it helpful to use plain full-screen color pages to check for corner glow, uneven brightness, or stuck pixels. A dark background is usually the easiest way to see clouding, while bright colors help reveal uniformity issues.
I started using a small browser-based color page for this. It loads quickly on Windows, macOS, tablets, and phones. Nothing to install — just open the color you need and switch to fullscreen mode. It's especially useful right after unboxing a new laptop to see whether the panel shows any obvious issues.
This is also handy for comparing different units of the same model, since the differences in clouding or brightness uniformity can be quite noticeable.
For anyone who wants to try the same color screens, here is the page I used (enter it manually in your browser):
pinksceen[dot]org