The difficult one with the green squares challenges us to find the difference between 4FBB0E and 5FC004. It's a pretty substantial change in the red value (though totally invisible to me). They cover themselves in ochre, right? So they're probably more sensitive to red.

Also, they screwed up producing the video. The first time they show the green squares, the different one is in the top left. The second time, it's in the top right.