Kuro - Vol. 3 Ch. 123.124

[MangaDex]

 

[DANDAN_THE_DANDAN]

This lines up with my previous hypothesis. The monsters are afraid of pure white but it doesn't harm them. Since human don't produce a lot of pure black objects, they can't feed off of them so why bother stepping out of your comfort zone if all the prey you need is right within your reach.

 

[Borderline]

It looks like the piece of monsters already get inside of the road.. I wonder if human can get infected.