So you're implying that if you changed the HTML colors based on mouse events, the claim of "difficult or even completely impossible for robots" would hold?

Such a claim would be no less ludicrous.

I'd put my money on there being hundreds of people on Hacker News alone that could script a DOM-monkeying cracker for such a system. That runs with ~100% accuracy. And in under an hour of coding.

This Captcha strategy is so absolutely terrible in light of modern libraries that I'm honestly shocked you feel the need to defend it.