Filter Fade Button

Hi, I have a fade button setup already and a slider for volume and filter seperate.
I was just wondering if I could have some help setting up a fade button for the filter also?
Basically just want a parameter to fade down over a certain period of time.
It would be also good if it could have a variable so that when it hits 0, my button can change colour and icon.

Thanks heaps! :smiley: