Eagle Vision is a sixth sense that some people have. It must be found and trained like any other ability that can be possessed.
Walkthrough
Arno begins with something more akin to a pulse of Eagle Vision. He can only have it active for a short time. It has a more limited range as well.
Colors
Various NPC's will appear different colors depending on their relation to Arno
Gold
This color is for the Targets. These are people or things you are looking for.
Blue
This color is for the Guards. They will only give you trouble when you cause a lot of trouble or attack people.
Green
This color shows you allies. They will help Arno if he is nearby.
Red
This color is for aggressive foes (like the Extremist). They actively attempt to pick a fight with Arno. They will also just attack him without much prompting.
White
?????????????????? I'm asking... I found a White Glowing priest in a graveyard and was able to pickpocket him. I found a note. ?????