Flangesight is a term for this. Basically, if your character is say... someone who can see things relating to dead spirits, and there is a character with "People who can see spirits PM for details." you should PM the character for information about what you'd be able to see.
As for what characters you can justify having them, it just depends on your character and what you want them to do.
Great, thanks.
Flangesight isn't just visual, however. Dark has a type of Flangesight that basically lets him 'smell' magic...
I've noticed a few roleplayers have bios saying that heroes with some kind of vision mode (I can't remember the exact name right now) should PM them for more information. What exactly are these vision modes, and what characters can I justify having them?