Cycles an all white panel between 0.5 and 0.0 opacity for a 2 seconds. Creating a visual flashing effect. Place a panel over an Max object and attach this patcher to it. You'll probably want to disable clicks for the panel.
Trigger the flash by sending a bang to the first inlet. Adjust the amount of time to flash by sending a number to the second inlet. Adjust the speed of the flash by setting an update time to the third outlet (lower is faster here).
I use this to flash a UI element that just recieved input from the outside world, Ableton or my MIDI controller.