I have a few gold necklaces that I know aren't actually gold but cost around the £25 - £35 mark so not as cheapo as say Primark. After I've worn them a few times the go much darker and dull I'm assuming it's some kind of reaction to my skin and the ones I have that are longer and tend oo sit on my clothing don't do this. Is there anything I can do to stop it? I really love the look of gold, but can't always to afford the real thing.