With a bit of modifying code to use the color picker and maybe rearranging the workflow to adapt to the new system, apps as advanced as DaVinci Resolve and LibreOffice can have permissions as restrictive as this (the network permission would of course may be needed but it would still be marked as Safe by Flathub).

You can use the file picker API to open the files or folders your app would need to access while having no filesystem permissions at all. You can access the camera, microphone, and GPS without the user devices portal, by simply using the respective portals where the user has the power to allow or deny access to such devices as they wish.

You can record the screen, take a screenshot, and pick a color in the screen by simply calling the proper portals, with the bonus that the user will be able to select if they want the entire screen, a specific window, or a specific area to be recorded/captured and whether the cursor should be shown or not.

Heck, even TeamViewer can be as this restricted without losing any functionality if they use the Screen Cast portal which allows apps to mirror input from a remote device! They would of course need the network permission, but that's still safe.