Why when i change the transparency of a prefab in runtime it change the prefab permanently?!

i change the transparency of color of Sprite Renderer in runtime and it saved the changed transparency after game view on the prefab!!!why?!what can i done to prevent this?

All changes you perform on the prefab are permanent, perform changes on the instantiated object of the prefab instead an hit “Apply” if you want to apply the changes to the prefab.