I think foil would definitely be better than nothing. Water, being one of the best solvents we know of, will take up gold and silver atoms from the foil. direct skin contact will also be beneficial I think. Certainly help one sell it if that were their goal lol
Colloidal silver, I make myself. Colloidal Gold (actual pure H20 = AU ONLY), is a noticeably different process. My opinion is, go with the nano particles for anything other than an extra 9 at the end of the 99.999% of things soap kills.
If you want to sell it, foil would definitely make it easier to believe they're in there. They'd look amazing on a sales table I bet. But that's where you start losing "freedom" when it comes to the words you're allowed to use.