Use System-wide color picker in iOS 14
iOS 14 introduced a new system-wide color picker (similar to macOS) that allows you to save colors to use across apps and includes an eye dropper tool. This standard color picker should replace the custom one currently used in GoodNotes.
For more information, here is the Apple Dev documentation: https://developer.apple.com/documentation/uikit/uicolorpickerviewcontroller

Thanks for sharing your feedback. We have already looked into the native color picker of iOS 14 but have decided not to use it because it limits our flexibility in terms of new features we may want to add to the GoodNotes color picker. We will add a +1 vote for you on adding an eyedropper.