What do the City Border colors signify?

In a region I can see each city has a border outline, some are green, yellow, blue, black and my own is white. What are these colors for? Is there a master-list somewhere?

The Manual doesn't list them at all.


Looking around various regions, and seeing the 'blue' borders suddenly gone now, I believe I have figured out what they mean:

  • White = You are the Mayor
  • Black = Mayor is offline
  • Green = Mayor is online and in this city
  • Yellow = Mayor is online, but in different city

At launch, there were some colored blue, but that may have been a bug perhaps with server issues.