This is a pretty personal request, but others might agree.
I never play co-op. That means I never have to decide if that body over there is a friend or foe, it’s going to be a foe, shoot it.
In BL3 there are many more missions/activities where you’re paired with NPCs who help you in the battle (and I don’t mean like Kill stealing Lilith in the Firehawk lair ), they are Good Things.
However, I constantly shoot ‘em. There is a body running over there, shoot it, then realize it’s one of your allies. Take some fraction or more of a second to realize that you shouldn’t be a-shootin’ em.
Enhancing their freind visibility would be nice. Maybe a blue aura around the whole character, or a large green diamond over their head.
Just a thought, not a big deal but I do waste bullets and time shooting my allies.