Creating 'Flashing Effect' using final cut pro?

I want to create a flashing effect using Final cut pro similar to one of those epilepsy gifs circulating around the internet eg. (do not view if you have epilepsy) http://media.photobucket.com/image/seizure%20gif%20white/endedcircle/stems2****/ Seizure.gif

However I would like to flash white and then a movie and then back to white. So it would keep flashing the white, but there would be a movie playing in the background that you can see only by concentrating? What is the best way to do this?

This is my first project on Final Cut, but I'm thinking something to do with different video tracks?

Cheers, Really appreciate your help.