From personal experience I can tell you that old Rolex yellow gold watches have a very different look from anything else. Rolex reportedly used an alloy composition that favored copper (?), creating a rich, warm red gold tone. Disclosure: when I was a young lad, back in 1978, I wore a fake gold Rolex President with bark bracelet. I had a (horrible) fake, which was all that was available way back then, and had it gold plated. I threw money at it to make it better, but in the end, the gold tone alone was a giveaway. Owning a gen Rolex for 8-1/2 years now (which I will sell very soon), I would not want any gold-plated fake to be a solid-gold pretender. It's just too much.
On the same token, there are watches that require the whole package, namely Patek Philippe. Kids don't wear Pateks. Ralph Lauren wears 'em, CEOs of companies wear them, so it's a certain clientel. If you drive up with your Honda Civic with carbon fiber rear wing, wearing a Patek, any Patek, I can be 99.99% sure that it's a fake. If you step out of a new Rolls Royce Phantom, I can be fairly sure it's genuine.