Is there any sort of addon that you can configure the color of the agro aura (arounds a mob's health bar) that the normal WoW ui uses?

I would like to configure it so that the aura glows Green when it's my target, blue when an OT has agro on it (which I would be able to configure) and Red when anyone else has agro on it.

Are there any addons like that?

dno but if you find one post link in this thread

There are a few nameplate mobs that allow you to get some slight differences with the aggro aura around the mob healthbar.  caelNamePlates is one of them.