Weapon Skins Thread

[WeaponTheory]

Raven Down Weapon Skin.

How does one get this? Because I checked my skins for my Gnasher Shotgun and noticed that I some how got this, it doesn't even show a preview image of how it looks. It just says "Custom Skin". But when you equip it and see it in-game, it's like bright orange or yellow or something.
I only got this skin for my Gnasher Shotgun.

How the hell did I get this? Because the other day I checked my weapon skins and never saw this until today.