I believe it's the same effect as in https://observablehq.com/@fil/black-and-white-colored-castelo ? Very cool!

So I have protanomally... do you think this could be exploited to "see" colors that I normally can't? :p

Oh yeah! @fil it's exactly the same effect :) that's a really cool example! And @jobleonard, good question! I added a section at the bottom that allows readers to pick custom colors and try them out, if you find any surprising combos, let me know!