There are two different cases I can make out from your question: 1. Detect if some material changed. (Not possible with ElementObservers)
2. Detect if the material assignment of some element is changed. (You get a APINotifyElement_Change notification for this with ElementObservers)
I think you want case 1 correct? I came up with a technique on how this might be possible. I use it for something else so I'm not 100% sure it works for this case as well. So try with care. Here's a rough sketch: - Make sure "Save each step" is enabled in the Data Safety settings of the AC Work Environment
- Use the Project Notification "APINotify_TempSave"
- Now you can check on every action whether your material changed (API_Attribute stuff) - this now is triggered on almost any action in AC so be careful to not use to much time to decide whether to act on it!