Potions cannot be used as items - they cannot be put on or removed as you desire.
If you wish to change your skin tone again, you'll have to buy a new potion.
The only skins you can remove as you please are equipably items.
Basically, if you have to go to your "special" tab to use a skin, it's not removable unless replaced by another potion. If you can put it on from the Dress Up page, you can put it on and remove it as you please