“Fader” first appeared out of NERD in their Pastel animals. Around the same time, in the completely unrelated ‘Citrus’ Pastel line from independently imported founding stock, the “Whiteout” appeared. Also around the same time, also in the completely unrelated Graziani Pastel line from independently imported founding stock, the “Duper” appeared.
All of these first appeared in the superforms of each line. Over the course of a couple season, the single-gene forms from these lines began getting the label.
Now… What we have is either:
A) Three wholly independent and unrelated WC founder stock lines that all had some secret gene hidden in them which magically expressed itself in all three lines all at the same time.
B) The constant selective pressure for higher-blush, higher-contrast animals by the founders of those lines, who all got them around the same time, resulted in a similar (but not identical, because of different selective criteria by each founder) polygenetic phenotype being expressed among all the different lines.
The founders of two of those lines, when breeding their trait exhibiting Pastel animals to non-Pastel animals, recognized that the trait basically disappeared. The third founder bred his trait exhibiting Pastel animals with another morph, that he had also been selectively breeding for high blushing and contrast. Unsurprisingly, the offspring from that also displayed high blushing and contrast. And from this, it was decided that a new secret gene/morph had been hidden in the original Pastel animal.
We no longer see animals being sold and carrying “Duper” or “Whiteout”… But we still see “Fader” (or poss “Fader” or "from a poss “Fader” or "might also be “Fader” or…) 
Fader is a line bred traits selected for higher blushing and overall higher contrast animals originating from NERDs Citrus line of Pastel.
It is typically characterized in its most subtle form as a flame of blushing somewhere down the second half/last third of the body that flares up to the back of the animal, but doesn’t cross over the spine. 
Fader is a polygenetic trait. It’s not a simple dominant trait and will not be passed on to offspring in any reliably predictable manner.
To add more confusion to this trait, the term “Super” Fader had been used by some breeders to describe high expression animals. Causing unknowing members of the community to believe that Fader is an incomplete dominant mutation, as homogeneous inc-dom mutations are usually prefixed with the term “Super”.
This in turn leads to offspring from these animals being labeled as “Fader”, when in fact they do it display the desired line bred traits.
No known proven lines