That original half-black/half-white caster for very simple/cheap optical limits was something of a known off-the-shelf approach. You'd often use them in various Lego Robotics environments a decade or two before the Roomba.

It's easy to agree with the article here that the off-the-shelf simplicity of the early Roomba was a virtue. I appreciated that sense that you could look at a lot of the parts and guess what they were for or how the operated from the software side. That caster was one of those for "oh, yeah, that's probably for simple distance estimations".