It may well just be gold-toned stainless and all you're seeing is the gold coloring wearing off. Should work equally well with or without the color. The whole idea is not to impart or transfer flavors and stainless will work well.
It's not like you're exposing the filter to any complex chemical interaction (like frying chicken in copper/brass), you just don't want to affect the flavor.
if we are talking coffee filters... the gold on mine, l ike Elvis, left the room at least 5 years ago!
Have not seen any difference.
I might add I use "Urnex" on a regular basis to clean all my coffee and espresso equipment. It's mean stuff! -- I think that the gold left us on jsut about the first use.