Wow Cata, there is even a physical explanation.

Only:
I'm not an expert in physics, but me thinks there is a problem. Me thinks that there isn't much ultraviolet light around us, since it's easily filtered by objects, much easier than normal light.
So if you can see light in the ultraviolet spectrum, it doesn't help you very much.
So much for physics in EQ :)

I've the impression that they chose the name 'ultravision' only because 'ultra-' sounds like 'more'.