A: An API key is gray in the settings when the user it belongs to is inactive. Apps that each user activates for themselves get one API key per user. That key belongs to the user and is listed as user name - app name. If that user is deactivated, the key turns gray. It becomes active again if the user is reactivated. An API key cannot be activated on its own.
When an app is deactivated, its API key is removed from the list. When you activate the app again, a new API key is created for it automatically.