I have just played my first two missions with this feature... it is absolutely amazing!
I am never gonna play xcom without it, ever.
Bless you Unknown Hero for suggesting it... bless you, your children, their children and all their descendants for 10 generations.
Could make a Pull request of this feature into the Master tree by SupSuper? It sounds amazing.
I do not think Green is a good idea, even thou you could see it as a indiator, i can probably shoot those Aliens without fearing reactionfire.
Maybe you diversify those even more ading a third color.
Red - Aliens directly in Sight as usually
Green - Aliens visible by other Soldier, but selected Soldier has a valid Line of Fire.
Orange - Aliens visible by other Soldier, but selected Soldier has no valid Line of Fire.
That should basically handle all cases i guess