This is a simple fix. Make shaders a collection in the vault. Make it so they "unlock" instead of drop and then when you go purchase one from the collection it asks you which item you want to put it on. They could even be cool about it and offer a discount for shading your entire character in the same color or something. It's really not that complicated Bungie!!
Or hell just stop being stingy and figure out a way to give us unlimited vault and inventory space. Obviously there can still be caps on quantity for certain items. Man, maybe Bungie should send me a check cause I just did someone's job who currently has there head firmly planted in the sand.