When gold plated sterling silver chains tarnish, does it reveal silver underneath, or does it look bad?

Thank you for asking, Gemma. Let’s face it. When gold plated sterling wears even a bit, the silver begins to peek through. There is nothing attractive about that. Gold plated sterling does not tarnish very much. It simply requires a gentle cleaning.
Most gold plated sterling is flash plated with a micro-thin layer of gold. The gold is gone at the beginning of normal wear on the piece. There does exist heavily plated 24k gold over sterling. It gives that desirable, warm yellow of high carat gold at a lower price, but it is not inexpensive. Still, there is the eventual wear factor.
I have noticed that gold plated sterling is being praised on the jewelry channels on television for its fineness and its quality and value. Fakat, we know better than that.
Vermeil (pronounced ver may’) is also gold plated sterling and it has an exact standard of the amount of gold plating to the sterling. It is also very attractive, but the wear factor still looms.
Buyer beware of gold plated anything. We all know what is eventually going to happen.
What is better 18k or 24k for gold plating?
technically both are the same. plating is a chemical process of putting gold on the surface of another metal. the chemical process involves making gold plating salt which is made with pure gold. the chemical process cannot bifurcate the gold getting deposited on the surface of any metal by lower or higher karatage. the gold getting deposited is pure 24 kt gold. the color varies, upon request, by tweaking various parameters like time / temperature / current etc, to arrive at the correct color which usually ranges from 10 kt light yellow to deep yellow of 22 kt gold.
hope this helps.