If a toggle isn't possible then how about a helmet instead that just looks like Vella. This sounds crazy but it is actually a good idea. I know enough about Blender and Maya modeling to know that something like this is definitely possible and can be made to look decent.
It would be bald so whatever hair is equipped would show through. With 5 possible dye channels it wouldn't be that hard for players to match up the skin colors with the body. It might have to wear a choker though to hide the seam of where it connects to the body. But this is definitely doable. It is just a matter of convincing the devs to make it happen.

