I ran the frames of that gif through a canny edge detector to see if that might be another thing that could help with region selection/masking. I'll have to play with it a bit and also figure out how to do it in photoshop (I just ran it through matlab's built in tools with the default settings) but it looks promising. I put the output images back together into their own gif because it looks pretty neat:
edit: black-on-white might be easier to visually parse: