I am not opposed to mixing metals, however, I agree there are some cases especially if you are using statement jewellery where it might look too cluttered or messy.
I think if done right mixing gold and silver necklaces for example can add interest to an outfit in its own right.
It's much easier when when wearing a single statement piece is composed of mixed metals...which pulls together any additional pieces you throw on. Ex: the necklace above, Rolex watches, etc.
But it depends on the finishes and aesthetics. Pieces with similar aesthetics, as well as tarnished metals work more easily together. Also, gold+diamond pieces mix easier with silver and platinum because the diamond emits a cold, silvery glimmer.
I always mix. It's a bit granny to match everything.
I think so too but I think most people look a little better in either silver or gold and should stick to one or the other. Wearing a lot of one metal can actually be a sort of statement, especially if it's skin flattering. Sometimes I opt not to wear a necklace and just go with earrings and a ring or some such combo. Today I am full on granny but my earrings have yellow glitter on them and are more like little art pieces than straight up silver earrings.