- "Eh, see, what you feel, the haunted look in your eyes, doesn't come from nowhere."
"Then where does it come from?"
"In the center of your being, there's a tiny beating heart."
"What, you mean like my soul?"
"Part of it, yes, the slimmest part, but it holds specific power."
- —Martin Chatwin and Julia Wicker[src]
Shades are the part of the soul that makes people process complex emotions like love and pain, and are responsible for the development of empathy. Shades are responsible for feeling emotions to their fullest, meaning if a person becomes traumatized, they are the reason you feel agonizing pain.
Little is known about Shades, and most information is heavily related to religion. Shades are not a common knowledge among students, but may be at least told about by the time a Brakebills student graduates their course.
Described by Martin Chatwin as "a tiny beating heart" in the very center of your being, Shades are what make you feel the most intense of emotions, including the kind of pain that seems as though it will "burn until you're nothing", but Shades are also responsible for love, as they are what make people 'human'. Shades are heavily connected to an individual's sense of right and wrong, and form the emotional connection to morality. It allows people to process complex emotions and connect to one another.
Upon removal, a Shade goes to the Underworld and into the Elysium providence for their eternity. For a dead individual to rest in peace they must have their Shade, though this may be arranged post-mortem.
When a Shade manifests outside of a person, it appears as a younger version of that person (approximately 12 or 13 years old).
An individual may remove their Shade out of choice, but in some cases, individuals may lose their Shades through magical circumstances. While they won't die, their emotional capacity is almost non-existent: they will be unable to truly feel or have empathy towards others, and thus become less hindered by moral repressions. They no longer feel pain, regret, fear, shame, or even love. They see the world in a very logical and straightforward way, willing to do anything to accomplish their goals. Shadeless individuals seemingly abandon their original personality, becoming unconcerned with the consequences of their actions.Julia Wicker described the feeling of being Shadeless as feeling incredibly light, as though a weight had been lifted off of her, feeling tremendous relief from her previous trauma and pain. Shadeless individuals do not process emotions in the same way as others, but they do still maintain emotional responses, as Martin Chatwin and Julia regularly laughed and smiled as they made light of serious and life threatening situations, going so far as to be willing to kill and sacrifice former loved ones with no hesitation in pursuit of their goals. One of the show's creators, John McNamara, described Shadeless behavior as being "sweet as ice cream, but twice as cold".
Shadeless individuals are not all inherently selfish or evil. Julia, upon realizing what being Shadeless meant to those around her, had to consciously reflect her actions based on her memories of emotions and feelings alone. Despite its difficulty, she began to carefully consider her actions and their consequences to try and help others.
Many Niffins are believed to be bloodthirsty and impulsive as a result of their lost Shades but some, such as Alice Quinn, simply follow their desires, be it freedom, knowledge, or power, with no consideration to the consequences of their actions.
Shades can be removed in pieces or as a whole. The slightest removal will evoke a significant change in an individual's personality. Shadeless individuals are able to hold the Shades of others, as with Julia carrying Alice's Shade inside of herself briefly. In the Underworld, Shadeless people have a large hole in their abdomen that slowly closes. The longer a person goes on without a Shade, the harder it is for them to regain it, and eventually, once that hole in their soul closes, they'll be unable to return to their original selves.
A deity is capable of placing "seeds" of magic within shades that can be infused within their counterpart once reunited. This grants the human a spark of magic that can grow to the point that the human is elevated to the level of a deity. As punishment for his crimes, Persephone took Reynard's magic and placed it within Julia's shade, as a gift for sparing her son and to aid her in her quest to bring back magic. Julia grew this "seed" within her until she became a deity, "Our Lady Of The Tree".
- Martin Chatwin - By choice. 
- Julia Wicker
- (Book) when assaulted by a god.
- (TV) as a complication of an 'exorcism' involving her unborn demi-god fetus; ultimately restored.
- Quentin Coldwater - In the 23rd timeline, Quentin was killed by The Beast, who tore his body and shade apart. In the process of bringing him back to life, Alice did not restore his shade which lead to terrible consequences.
- Niffins - In the process of becoming a Niffin, an individual will lose their shade.
- A Shade can be equated to "the heart" of the soul, as opposed to the soul itself.
- Shades in the Underworld act as 'guardian angels', performing minor miracles for people.
- Humans lose their Shades upon transforming into Niffins and cannot be reverted back without them.
- Patrons of the Underworld have jurisdiction over the Shades in Elysium, and can even bring Shades from the Underworld, as shown when Persephone reunited Julia Wicker with her Shade.
- This could be a reference to the more classical forms of mythology, with Hades being known to return the souls of the dead to adventurers like Odysseus.
- In classic Greek mythology, shades were the spirits or ghost of a dead person and another name for the Underworld was "the Kingdom of Shades"