Another technique for tuning into the perception of horizontal motion: Use your hands or forearms to block your view of most of the picture, leaving only a narrow horizontal slit. For me the effect persists upon expanding my view to the full picture again. To 'switch back', look at a thin vertical strip of the picture for a moment.

As soon as I manage to see the motion as left-to-right, the dots look yellow — though the impression is really close to flickering between red and green. How readily your visual system will merge individual strobes into a coherent, moving visual impression depends a lot on how awake/alert you are at the moment. So you could also try again when you're more tired. Another thing to try: Change the playback speed to 2x. Though I'm not sure if that will increase the frame rate to 60Hz or skip frames. In this case you want the former; it may be necessary to download the video and play it back locally to achieve that.

By the way, I once managed to produce a similar illusion completely by accident: I had made an engine for rendering totalistic 2D cellular automata (a superset of Conway's Game of Life) that randomised the state-transition rules upon a keypress. After a while of browsing random rules, I found one with a tendency to produce neat tiny gliders: A sequence of three distinct colours (and therefore states, I thought) racing across the screen — something like a cyan dot trailing a purple one behind it, with a pink one sandwiched between them. But then I looked closer and saw that the pattern was only two cells wide. Taking a screen-shot and looking at the freeze-frame confirmed that the gliders only occupied two neighboring cells, with two different colours, at any given point in time.

Try following a region on one of the lines moving strictly horizontally to the right with relaxed vision (not focusing precisely). Choosing a point close to the top of the lines should be easier.

At around the 0:15 mark, two overlays come on screen, creating an open column in the middle and two horizontal channels at the top left and bottom right. I noticed that I was seeing both options: yellow lines moving horizontally across the top left, turning into downward-moving red and green, then transforming again to yellow as they "turned the corner" at the bottom channel.

I wonder if those horizontal spaces will help you see the yellow.

I saw the up/down initially, but now I can only see the sort-of-yellow left-right unless I close my right eye. The vision in my right eye is vastly more blurry than my left (thanks kerataconus!) and I suspect the blending of the red/green is more pronounced for that eye.

It may depend on the screen tech you’re using. It relies on persistence of vision to merge the red and green dots into yellow when tracking horizontally, but it wouldn’t work on too big or too small a screen, and might not work on pentile displays.

Try and lock onto a dot as you track your eye from left to right. And then to undo that, lock onto a dot as you track downwards. That's how I managed to switch between red/green and yellow dots.

It is much easier to see if you do not fullscreen it. Keep it relatively small, and if you still don't see them, unfocus your eyes just a little bit. Good luck!

Try bluring your vision or moving further away from your screen.