I´m using a notebook with nVidia Optimus, so I can tell you something about the behaviour of both Intel and Nvidia graphic units!

To imagine how this looks like I´d suggest it to be comparable to something that causes epilaptics: RandomScreenFlashing and so on.

The hard part is: I wasn´t sure at the first moment whether this was intentional or not, as the general design formula this game uses would even think about using such flashes like that---> but it was so hard I had to quit after two minutes!
Those flashes don´t appear on Geforces and proberbly they aren´t there at Radeons, too!
So: If anybody only got an Intel HD 4K: Please wait for new drivers!

I'm on a Surface Pro with an Intel HD4K; just played through the first room/level and I haven't seen any screen flashing as of yet. I've heard of graphic anomalies occurring with dual graphics setups, which are usually solved by forcing the game to use one of the two. Not sure exactly how that's done as I don't own one.

I'm using an Optimus laptop with a GTX 660M and intel hd 4000. I ran the game with each card and there wasn't any flashing. Alt-tabbing out and back into the game causes the graphics to start flickering - not flashing like you describe, but worth bearing in mind I suppose.