It is unclear what you are asking. What you are asking sounds more like using something to add color to the monochrome on the screen, like the Magnavox Odyssey [1] or the Vectrex [2]. But that would be orthogonal to what this is doing.

[1]: https://youtu.be/Lc8swrtGer4?t=211

[2]: https://www.youtube.com/watch?v=uz3QAj7I3MQ

I think they mean that rather than have the RGBI splitter hardware, have a full-signal splitter that displays the same full color image on each monitor, then put a color filter sheet on each monitor to only pass a specific color.

It would have the benefit of working with NTSC, PAL, composite, and other output signals that don't breakout RGBI components on separate pins. But it would have the downside of only supporting 3 monitors instead of 4 (can't color filter on intensity). And of course each monitor would look red, green, or blue according to their filter.