Qt provides cross-platform support for picking colors on the screen via its QColorDialog which has a button "&Pick screen color". This takes into account platforms like Wayland (see https://bugreports.qt.io/browse/QTBUG-81538) but has also hand-made support for Windows and works fine on other platforms.

It would be great if there were a public API to access this functionality that is yet existing in Qt. Something like: "Call the API (which will itself take care to display the crosshair cursor and so on) and simply get the user-selected color in return (if any)".