[Baertram]

As far as I know you cannot add some visual effects to the players or chnage the textures of their armor etc.
So there won#t be any possibillity to "highlight" them.
You must read the chat to see who wrote something or build an addon that tracks the chat say and group channel for a playername writing some special word like "rez" and then show it on a new small window on your UI where the player's name would be listed and blinking. Maybe with a timer difference since he wrote the word rez to the chat and the time now.

What could be possible is that you may change the texture of the icon above their head, but you cannot change the color!
You could then cycle some different textures above their head, changing every second, so you could notice them. But they will stay white!
I'm not sure how to do this, maybe the author of the addon "PapaCrown" got an idea.

In both cases I'm not interested in doing this addon as I don't think ppl say "rez" to the chat. In my opinion they just say it into teamspeak/ventrilo or you, as the healer, decide whom to rez as priority. Teach your ppl to not go away during fight and you are fine :-)