This is by design. The icon is green and displays a locked padlock when you are a standard user. It looks like this:

The icon is orange and displays an unlocked padlock icon when you are an administrator. It looks like this:

Yes. By default, administrator privileges are granted for 20 minutes (if not configured otherwise). However, if necessary, you can configure Privileges not to remove administrator privileges by setting the expiration interval to “Never”.

Yes. You can set a time after which the administrator rights will expire in the settings.

In this illustration you can get an overview of how the different app components communicate with each other: