Let's say on the second wall, instead of graffiti of violence, you see a message of love. You look around the wall and you see there is a person in love, a family sharing love, a town with flowers, a peaceful city.

For a wall with nothing, it could be a value in the set that corresponds to a particular color that represents it did not meet the threshold.

For the first sentence, my point was not to imply that a presence of one kind of behaviour leads to similar behaviour in related structures, but that at different scales, components of each structure may exhibit similar kinds of behaviour. E.g. a person can be considered to be violent or peaceful and so can a community. This could be from our nature of finding patterns in everything, though. Which I guess also leads to emergent properties anyway in some way, so I cannot add much more there.

Actually I am unsure if it fits the definition of emergence - "emergence occurs when an entity is observed to have properties its parts do not have on their own" - but it would be hypocritical for me to argue on that note :D