I told this too, but it seems you overlooked this part. *sigh*
1. Every race have "their" systems in the Report screen. But this list have one serious omission: shared systems are not on this map. Even if opponent have _one_ planet belonged to other race in the system, this system will not show at the map of either opponents. Looks like the bug for me: in reality it must be shown on both maps.
2. Every such shared system is effectively "invisible" at the main map too. All of them have white color, and doesn't allow to detect at glance who is under this whiteness. So proposal: can you color shared system with all involved races? In mentioned Space Empire 4 it was simple but elegant: every system on the map was a color circle like a pie chart, and amount of every color was simple representation of different races' share. Of course, you have squares... but you still have 4 corners!
What about coloring it accordingly to represented races? (no shares but, oh well, you cannot have everything! Also, you still can use pie charts in the Report screen... but I am too engaged here, I know.)