I had read somewhere, a few years ago, that one should not use a gold cup for the 4 cups of wine at the Seder. I don't recall the source but I recall that the reason mentioned is that it is considered "pompous".
If someone can confirm or deny this rule from a source, I appreciate it. I'd be surprised if using a gold cup is forbidden as IIRC, the Shulchan Aruch mentions that the Seder table should be set with the finest and nicest things that people own, so why not use a gold cup? Related to this, perhaps, is that the Torah says that Israel left Egypt with gold and silver. So, wouldn't using a gold cup on the Seder be a way of commemorating what occurred?