This is so cool. For your figures, how did you decide the RGB colors of the 4D colorspace? Or did you convince ACM to print your paper with special inks? :)

Definitely not the latter as the paper mentions "The digits are faintly visible in this photograph, because the camera’s color response differs from a human’s."

I remember watching a video some years back where the researcher thought he had developed such a test.

As I recall (it's been many years; likely over a decade since I saw it) he tested it with a woman who was believed to have tetrachromatic vision. She could reliably tell the difference.

As a control, he tested it with a man who was trained as a graphic artist.

He too could reliably tell the difference.

That result strongly implied the test did not work as expected.

Do you know anything about this previous work? I tried reading the paper but was immediately out of my depth.