Changes made during play mode, remain in editor after the game stops

Searching for my problem reveals questions about changing something during play mode and having it save in the editor. This is the opposite of my problem - I want the changes during play to revert back to before i pressed play when i stop the game, just like what normally happens. Here is my specific issue:
A script runs during play mode, that fades in a background material from 0 Alpha to 255.
When i stop the game, the alpha value remains at 255 for the material.

This really confuses me as i am fading in all my game objects over time and everything else works fine - they fade in and remain opaque throughout the game but start from 0 alpha next time I run it.

I am completely lost and would appreciate any help. The only difference i can see with this GO compared to the others is that its material uses its own single texture, while very other GO uses the same spritesheet.

You should use material rather than sharedMaterial as changes to project items are persisted between play and edit modes. sharedMaterial accesses the project item while material makes a runtime copy. Scene items aren’t persisted between the two modes.