I'm assuminig it's an unfinished feature or a leftover since the only color it shows is white for me. However, I'm just curious as to what that color mode would show if it were working. Like the way velocity and acceleration show thwr respective values/properties, what would physics group show?
My speculation is that maybe it functions off of the relation lines and shows what is gravitationally connected to what (not neccesarily in orbit), or is being gravitationally affected by a specific larger body.
I did do a search and it hasn't been mentioned or discussed before, whether in the forums or in the changelogs.