The Lighting Controller

How do I make a flash scene that will strobe all fixtures regardless of what scene or color they are on?

Make a scene that only activates the strobe function for your fixtures. Save it and then input it into Live, then right click the button and make it a Flash button. Viola! You have a strobe flash button. And if you right click it you have a host of other modifications of that button to suit your particular needs.

I use two strobe scenes in my show: a general strobe, and later a generate a random strobe using the shutter channel for all the fixtures, put in in GENERATOR and make weird stuff with that to get a beatiful random strobe to give more impact to your show