Gold plated necklaces have a reputation for being the cheat's version of the real thing, something you buy knowing it'll turn your neck green within the month, and for a lot of the high street that reputation is fair. I've had plated pieces that lasted a single damp bus journey before the colour started lifting at the clasp. But a properly made one, worn sensibly, can look just as good as solid gold for a fraction of the outlay, and I'd rather have three decent plated pieces than one that never leaves the box out of fear.
The difference between the one you keep and the one you bin shows up fast if you know where to look. A thick, even layer of plating over a sturdy base metal, usually brass or sterling silver, will hold its colour through normal wear, while a thin flash coating over something cheap goes patchy within weeks, especially near the clasp where your fingers and perfume both get at it. Check the clasp itself works smoothly and isn't flimsy, because that's the part doing the most physical work, and run a finger along any chain links or pendant edges for roughness, which usually means a rushed finish. Weight matters too. A necklace with a bit of heft to it generally means more metal and better plating, not just a trick of the light.
Once you've got a good one, it does a lot of quiet lifting in an ordinary wardrobe. A fine chain sits well under a crew neck jumper in winter, peeking out just enough, and against bare skin in summer it catches the light in a way that makes a plain t-shirt look considered rather than lazy. Layer two different lengths with a simple top and you've got something that looks put together without any real effort on your part. It holds up for most of the year, though I'd keep it away from the sea on holiday and off before a shower, since chlorine, salt water and perfume are the three things most likely to shorten its life.
For occasions, it earns its spot anywhere from a Tuesday desk day to a proper night out, which is part of the appeal, it doesn't ask you to dress around it. Cold weather suits it best for longevity, since you're layering over it rather than exposing it to sun cream and sweat all day.
If you're starting with nothing, go for a simple yellow gold tone chain in a medium length. It's the one that goes with everything else you own already.