Systems with multiple owners used to be displayed like the attached image-- The text color divided evenly among all empires who have planets in the system. At some point it got broke, but it is IMHO, a much preferable way to display this info.
Currently the only the players color is shown, giving no indication that he is sharing the system with possibly hostile empires.
Multi-colored labels, won't tell you who owns the shipyard(s) homeworld(s), or capitol(s!), but trying to communicate all that would be too cluttered. The multi-color approach gives you enough info to know to check it out in the sidebar to see who exactly owns what, when you don't remember.