Basically title, just like you can change color of frame if they have poison, mind control etc I would love if I can change color of the frame if a friendly player is not in line of sight.

You can change the color of the frame when people is out of range (linking the range status to the health-bar color), but not when the player is out LoS, as far as i know this is not possible to implement (the game does not provide LoS information for addons).