lifesight

Lifesight, sometimes called "deathsight", is literally a different way of looking at the world as opposed to what most normal mortals and animals see with their eyes, aka normal sight.

Manifestation

Lifesight resembles normal sight but living things are easier to see and non-living things are difficult to see. Beings with lifesight are likely to stumble and trip over rocks and the ground and otherwise miss non-living things that normal sight can catch easily. Reading from a page is almost impossible unless something is written in blood, even then it's not easy.
For non-living things, colors and textures are extremely muted, practically monochromatic and somewhat dark.
Living things, plants, animals, and mortals seem to glow. Animals tend to glow more vibrantly than plants and mortals tend to glow more vibrantly than animals.
Recently dead things have a faint rapidly diminishing glow. Mortals also leave a faint glowing trail behind them when they move. Someone with lifesight can track a mortal with this residual glow. It's relatively easy to follow a trail through an icy wasteland but it is almost impossible to follow such a trail through lush vibrant jungle.
Also, a mortal's trail looks pretty much like every other mortal's trail. If someone is being tracked by their life aura, they can hide their trail by running through a crowded market place and getting their trail mixed with other mortals' trails.
Undead creatures and restless dead have their own glow. Living creatures tend to glow with white light, undead with reddish light and restless dead with something resembling a modern black light. Fae and spirits glow with a refracted rainbow light. It is impossible to tell the difference between a Fae creature and spirit creature from their lifesight alone though more more powerful spirits brighter than weaker ones, and Fair Folk always outshine Sprites.
Under greater scrutiny, living things under lifesight have their health or lack of health displayed. Beings with lifesight can easily gage how badly a subject is injured and see obvious visible manifestations of illnesses and curses. Training and experience is often needed to differentiate between "he's very sick" and "he has cancer." Curses are even harder to differentiate.
Under greater scrutiny, someone with lifesight can gage one of the restless dead's strength of will, both their overall strength of will and their current reserve of temporary will.
Under greater scrutiny, someone with lifesight can determine if an undead is under tight magical control, loose magical control, is free-willed, or rogue. If the undead has a fluctuating power reserve (like a vampire who has a variable blood pool), life sight can gage approximately how full their "fuel tank" is.

Localization

Void demons have lifesight as their primary sight. Only the most powerful demons are capable of accessing what mortals consider to be "normal" sight.

Restless Dead, aka ghosts can switch between normal sight and lifesight at will. As ghosts linger in their restless state longer their lifesight gradually becomes primary and normal sight becomes more difficult to access.

Many undead creatures can access both normal sight and lifesight. A few are stuck with lifesight alone. Undead that feed on the living find they have trouble using normal sight when they are hungry.
Most free-willed undead can switch between normal sight and lifesight at will. Some older undead with mental instability have trouble transitioning between the two versions of seeing.
When it comes to undead lacking free will, they are usually equally good at both means of vision, or more accurately, equally bad. Most simple undead are not known for great visual acuity. Many rely on smell and hearing above their sight, both types of sight.


Mortal arcane necromancers can access a simple spell called "Lifesight" that perfectly mimics lifesight. It is often one of the first spell an necromancer learns. Many mages who do not focus on necromancy will dabble in just enough to necromancy to learn this spell and a few other utilitarian first circle necromancy spells.
Divine necromancers cannot access lifesight. The Nine either can't or won't let their agents copy a power of the Void.
Despite it's dark associations, lifesight can easily be a tool to help the living. Lifesight is useful for those hunting undead, and it can help doctors and healers diagnose complex problems. It can also reveal a ghost or undead impersonating the living though there are other ways to reveal this.
For unknown reasons, a spirit or a Fair Folk impersonating a mortal or beast has a normal living aura, not a rainbow aura.

Fooling Lifesight

Anything that causes blindness in normal sight will blind lifesight be they mundane things such as covering eyes with a blindfold or magical effects such as invisibilty.
Lifesight is supernatural in nature so any magical abjuration that will at least partially block or obscure a mortal's life aura.
Areas rich in life, such a crowded city or a lush jungle create something akin to sensory overload and makes it harder to fixate on a single target with lifesight.
Thick clothes will diminish a living person's glow a little bit, but a more effective precaution is to cake on lots of mud to block a lot of a living person's natural aura. Combined with a life rich area such as a jungle, a muddy mortal is practically invisible.

Type

Metaphysical, Supernatural