How to make a button color fade on press? (while user is touching it)

I'm trying to make my container buttons border color fade to purple when the user has their finger on it (shown on the Google button). And turn back to gray if they remove their finger. How can I accomplish this?

The button shouldn't stay purple. It's just onTapDown, then go back to gray if they remove their finger (onTapUp)

Is there a way to hook into all the gestures that Flutter supports? (See link below – I may make another question for this)

https://docs.flutter.dev/ui/interactivity/gestures

Thanks