If the bottom of the colony was rubbing on something before you moved it, or if you have black sponge (they are known to sting some people), I've seen the black spots form. It's almost as if irritation causes a callous of sorts. I'm sure there are other causes, too, but I think it'll be fine

.
What part of Norway are you from? My family (Flatness) immigrated from Norway. Supposed to be the flat part (but there doesn't seem to be much flat land in Norway

).