Oh, this is such a fascinating detail! This house was recently restored and while it was in progress the workers have found (possibly!) the original design and decoration of a facade. As you can see, it used to be decorated pretty colorfully! For some reason it was not possible to restore it in this manner completely so the conservators decided to leave this one detail on the facade as a document of past times and changes that happened to this house. I just love discovering such little details in my town!