Gray

It was the middle of the day, and the guards were already getting sleepy. Lately, almost no one used the southern tract, so they didn't really have anything to do. That was until they noticed a lone figure getting closer and closer. Waiting for the visitor, they drew straws to pick which one of them would have to deal with the stranger. As they finished, the unlucky one chosen, they looked back at the traveler. Their looks surprised the guards. Their cape and their clothes, their mane, and their fur, all lacked all of the Color.
The visitor was a Beteclaw. And a Gray.
"There's a beast in your woods. Right?", the stranger asked the welcoming guard as they approached the gate. Their voice was weird, lacking not only all emotion but also something more important. Hearing those simple words coming out of the Gray's mouth felt unnatural.
"Right, sir," responded the guard, not knowing if what he feels is fear or just being uncomfortable. He never saw a Gray before. And this experience made him sure that he never wants to meet another one ever again in his life.
The beteclaw nodded, his eyes either not noticing or not caring how much he creeps out the one he spoke with. "I'm entering your town to buy some supplies I'll need to kill it. Is that alright with you?"
Before the guard even processed the question he was asked, the Gray entered the settlement.

It starts with a sickness

For most people afflicted with the Fading, the only future is death. The sickness causes all of the Colors to leave their bodies, turning their limbs numb and useless one by one. Some have enough luck to get Honey Savior (flower), the only cure for the sickness, but getting one requires either enormous amounts of money or someone willing to travel far north through many perilous regions.
But once in a while, something else happens. Instead of slowly losing functions, the body of the sick one continues to live as before. And while they stay is alive, they also start to change, both in body and their mind. At some point, they start to feel the calling. And so, they leave their home to never return.
They become Grays.

Gray body, Gray mind

A person suffering from the fading begins to lose all of the Colors inside their body. Their skin, hair, and eyes turn completely Gray. They lose most of their emotions and memories. The family and friends become strangers to them. They leave, either because they start to feel the calling to hunt or because fragments of the feelings they still have left don't want them to see as their close ones suffer.

The Hunt

All of the Grays can hear the calling. It is an unexplained feeling that pushes them to move forward and find the Witchkiller beasts to kill. They prepare in any way they can, either by buying, stealing, or creating weapons. They start to gather information about the beasts closest to them. And once the call becomes too strong to stave it away anymore, they begin the hunt. Until their quarry or they are killed, they will follow their prey anywhere. Even to the depths of hell.
All of the witchkiller beasts are filled with the Colors that filled them when they killed the Witch. They are the most oversaturated beings on Urnketh. As such, killing one of them would again spill all of their Colors, oversaturating both the surrounding area and the one who hunted them.
But that doesn't happen to Gray. Once one of them deals a finishing blow to the beast, Colors, instead of creating a large explosion, will try to fill the Gray, covering their body completely. After a few seconds, such "coating" turns transparent and drips off the Gray like water. This ability makes Grays the only ones capable of safely killing the witchkiller beasts.

On the move

Because their bodies lack any Color, the Gray slowly absorb the Colors from the area and the items in their surrounding. This, in turn, means two things.
First, they need to constantly move, never staying too long in one place, otherwise, they risk turning the land Gray and endangering other people.
Second, any equipment or clothing they use starts to break down and fall apart after some time.
The more of the Grays are in the area, the stronger they affect their surroundings. Both because of this and because they don't really care about relationships, they tend to travel alone.
All of the Gray live on a borrowed time. While the fading, didn't kill them, living bodies aren't exactly adapted to life without any Color. And so, they are aware that they don't have much time (the Rockwings Grays being one exception). Depending on their species, their lifespan varies from being short to extremely short.

Becoming a Gray and various races

Depending on the race of the one afflicted with fading, the resulting Grays tend to vary.

Rockwings

As Rockwings showed up first when the Colors in the world were still fairly rare, their bodies already possess a very small amounts of them. Because of that, losing them altogether doesn't really influence their personalities that much. Gray rockwings tend to keep their old dreams and some still follow them, even during their endless hunt. Just like before they faded, rockwings tend to approach the hunt from a more patient side, taking years to kill the first witchkiller beast they hunt.

Beteclaws

Beteclaws tend to lose most of the fire burning in their souls. The sparks of their true passion and ferocity show up only when they start to fight. Their enhanced senses let them follow their prey wherever it tries to hide. They are the most common Grays to encounter (mostly thanks to their large population), and the ones who tend to survive the longest compared to the number of fights they take part in.

Huerustlers

Normally, one would think that Huerustlers, beings that use Colors as their lifeforce, would always die when they start to fade. And yet throughout history, there were a few of them who escaped that fate and became Grays. Once they start to fade, they lose their Colors very quickly, leaving only a slight shine inside of their bodies. Still, a body of a huerustler tends to absorb large quantities of Colors around them and because of that, they leave a trail of Gray behind them wherever they go. They are the most ostracized type of Grays, being banned from getting close to any settlement. To get a weapon, they have to craft a new one by hand by themselves or get lucky enough and find a traveling merchant.

Smeltsparks

As machines of war, Smeltspark's bodies are made out of inorganic substances. Because of that, just as they influence any other item in the area, Gray smeltsparks tend to quickly drain the Colors out of the metal that keeps them intact. Unless they find someone able to replace the parts that fall apart regularly or they decide to do something considered immoral (Assimilation), they will cease to function in less than half a year.
Compared to other Grays they move quickly after their prey, wanting to kill even one witchkiller beast before they die.

Humans

The Human Grays are the most emotionless ones. Thanks to the human disposition to magic, they are able to use runes and Color-based firearms, though using the Colors themselves is impossible even for them. Thanks to that, they have more possibilities when it comes to the arsenal for the hunt. Just like smeltspark Grays, they move more than the other Grays due to their short lifespans (about 1-2 years).

Reproduction:
There are some stories of Grays that don't lose their ability to reproduce. According to them, a child of a Gray and a normal person will either be born normal or dead.
None of the Gray feel any sexual attraction anymore or have any sex drive.

Names of the Gray

Once they fade and the hunt becomes their only desire, most of Grays forget their name. And as there is no one that would be able to travel with them for a long time without risking their Colors being sucked out, there is no one to remind them to them. As such, most of the Grays are just called "Gray" by everyone else.

The Gray and the Colors

Due to them becoming completely Gray, Grays are completely immune to the Oversaturation (geographic anomaly) of the land and its effects. They could traverse the most contaminated territories without any harm to their bodies. Their ability to absorb and neutralize any quantities of Colors could be even used to neutralize the oversaturation, although that process might take years or centuries. Or what's worse, it could completely devoid the area of any Color.
Similarly, Grays are almost completely resistant to the Color magic. Most of the force of the spells that hit them is immediately soaked up into their bodies. If not for the need to hunt the beasts, they would be perfect weapons against the Witches.
At the same time, Grays are all incapable of using Color magic, with only one exception, the Gray mage.

The village built by the Grays and the Way of the Gray

Apparently, according to old chronicles, there once was a village created by some Grays that were more resistant to their calling. It was supposed to be a haven and a place of meditation, a place where they could find a new goal in their lives. As one can easily guess, the village didn't last for long, both because the land turned Gray and it became a wasteland devoid of any living beings, and because the call of the hunt always got Grays at some point, causing them to leave.
The disappointed villagers understood that they can't fight their destiny. To ease their pain they created a Way of the Gray, a series of teachings and exercises that lets their kin train their memory and meditate on things other than the calling. Once they met another one of their kind, they spread it further. The Way of the Gray exists to this day and even evolved over the years.

He was bleeding, but so was the beast. This hunt was difficult. A subtle feeling of fear, an echo of a real thing, went through his body. It almost made him happy.
Still, he had a job to finish. He cut and slashed the creature before him. They were both breathing heavily. And, at some point, the beast fell. Its Hues covered his body, seeped into his wounds, and then lost all of their colors.
For a second or two, he felt gratitude towards the beast for this battle. For their shared struggle. Then, with the last drops of the Colors leaving his body, he stopped feeling it altogether. Gray and blank again.
He bandaged his wounds, picked up his weapons, and went to search for another beast.

Silver sheen

All of the Grays instinctively feel their incoming end. It depends on the individual, but just before their death (sometimes minutes, sometimes days), it is said that some kind of sheen appears on their matte bodies. Like polished surfaces, some colors start to reflect on them, bringing back what they were in the past. During that time, their memories, passions, and emotions, rush back into them, sometimes partially, and sometimes with their full power.
The effect the silver sheen has on the Grays varies. Those engaged in a battle could both improve or get completely overwhelmed. Those who aren't hunting tend to try to either fulfill some of their desires, return to their families, even if for a moment, or simply stop in their track, absorbing every senstation they haven't felt for so long.