Unless I am missing something, currently there is no easy way to determine if you have open borders or just peace with an empire. You have to go into your deals details to be able to tell the difference. I propose:



1) Showing the Open Borders status by some other symbol than dove and/or different connecting line style in the empire matrix in the Diplomacy main screen

2) When you hover over diplomacy on main screen upper left corner, you get a list of empires and your relationship with them. There, it should say OPEN BORDERS instead of PEACE if you have open borders. Since you can't have open borders without peace, it would make sense to say OPEN BORDERS there.

As I remember, since Civilization IV(or even III), open borders were always different from peace. Actually it was more important in that game, but even here this simple fix will be quite useful.