I think iOS app cannot get access to view from other apps. Did you see similar feature in any other app?
Is that an ironclad rule by Apple? That they don’t allow this because I know in Windows you can definitely have apps that use color samplers that use web browsers sampling colors outside the environment. I don’t see why this wouldn’t be allowed. It’s a color sampler. That’s all. It’s not changing the environment outside the app to accomplish this. Otherwise magnifier tools wouldn’t be allowed in iOS apps...which require access to the API to see outside of its own screen to resize elements to be called magnifiers.
And just as an example...Procreate does have a color palette by photo option...which allows it to “see” outside the app to take snapshots to create color palettes. Clearly, a color sampler in ASP that samples colors outside the environment is not only possibleI don’t see why this should be forbidden. But I suppose as a developer you have the right to ask Apple if this would be allowed. I don’t see what the harm is to simply ask.