This is a continuous version of the purple dots illusion. Keep staring at the crosshairs. Eventually, instead of a white gap rotating, you’ll start seeing a bright band of the opponent color.
Incidentally, you’ll notice that this opponent color is quite bright - it in fact appears brighter than the white background of your display! This is because you’re experiencing a Chimerical color.
I’m sure this has been discovered before, but I came up with this particular version.