Many weapon skins look shabby by design and I think it would be nice for people to be able to tweak them. I do realize the weapons might not have been made with that option in mind, but this is Fashion Wars now anyway, so… Another plus would be backpacks. Right now you can’t really modify for example the moth wings backpack.
My suggestion would be so that the weapons don’t get too ridiculous (that’s where legendary skins come in) that the base color would have to be some metal (so that you can have a weapon made of “gold” or “mithril” or “iron” or “steel”) and then you can have some colorful tint to it. Then you could dye your hilt freely.
Same thing for the backpacks. The base color should stay the same with tints or material changes.