I've implemented a similar effect in the past by creating a fullscreen black quad and fading the alpha from 0 to 1. Here is a simple example:
Code:
import viz
viz.go()
viz.add('gallery.ive')
blackScreen = viz.addTexQuad(parent=viz.SCREEN,scale=[100.0]*3,color=viz.BLACK)
blackScreen.alpha(0.0)
vizact.onkeydown(' ',blackScreen.runAction,vizact.fadeTo(1.0,time=2.0))