How the Hell did origin realms make finish effects

Finishes are like animated textures that can be applied to cosmetics but i have no idea how they done it (and no its not simply just an animated texture) (and it acts like a dye).. I am a blockbench pro (and have been using it for 4 years now) and i checked every corner of blockbench to see if their is any way how to recreate it... my best guess is that the server itself is contantly changing a custom textured dye on the cosmetic to make it animated.. but that might not be true considering the rescource pack files of origin realms