Comment by gk1
What are some striking examples from your experience?
BTW this is what I love most about HN - the surprising variety of people you can learn from, from billionaire founders to expat bingo-card geeks to Georgian-onion sellers to Dutch pro cleaners...
On a Light surface tiny stains stick out, on a dark floor tiny flecks of dirt stick out as if under blacklight, a concrete color with some smudge patern may get extremely dirty without anyone noticing it (which might also not be what you want) a dark floor with a pattern of tiny white dots can also look very clean while dirty.
Any porous material is a terrible idea, you get lots of surface area that you cant reach. Carpet, curtains, upholstery.
Gaps between things should be big enough for how deep they are. Tiny legs under sofas or closets are not useful for anything. Adjust the size of the gaps between wall panels to your favorite kind of insect or rodent.
The funniest one i've seen was a city with a lot of mosquitos where someone put giant neon letters outside under a roof. In a few days it was completely covered in highly active spider turf war dens enough to make a grown man scream. Apparently spiders love roofs and they obviously know flies like light.