I have a button in my interface that when clicked show a listbox so the user can apply a filter by those items she has selected. It looks like this:
My question is: How do I tell the user there is an active filter? The tooltip of the button will have a description of the active filters but I was thinking about a change in the icon or the border of the button. What color would you made the icon for when a filter is active and when it is not?
Edit: Screenshot of the top of the application where the button is placed (the button is in the middle after the three comboboxs: