Comment 4 for bug 898129

Here's an alternative proposal. The idea is to signal the parts covered by an enhanched building is marked with a green plus. The same plus could also be used in the building window along with the building it is enhanched to. It's a bit off-topic, but I find the current solution of showing the building it would be enhanced into a bit lacking. With the green plus introduced it would be recognizable as tied to enhancing buildings, so that it would be easy to figure out the meaning.

I am also fond of #3 above, expect I think the colors should be improved. I also think this is a better representation than the current, which would help players form a correct mental model. The following reasoning would be a lot clearer:
* The filled circle is the base area
* The ring around is the enchanched area which would be added to the initial one to make a larger circle.
In fact, this is the reverse of what the current solution indicates.