Originally Posted by
Ynna
Healbot (Vuhdo as well) has the clique-functionality built in IIRC. What it does is it bind each of your heals a mouse and (ALT, SHIFT or CTRL) combination so you don't have to press buttons on your keyboard to heal. I don't know if there's a way to disable it, since I don't use healbot.
Anyway, to answer your first question: the default raid frames do that. They become less green if a target is out of range, which is pretty much how raid-frame add-ons do it as well.
The most commonly used are Healbot, Grid and Vuhdo. Grid doesn't have the click-healing built in, so most users of Grid use either Clique or mouse-over healing.