First, you should know that gold plated jewelry will tarnish over time because of the nature of the metal that's more fragile and susceptible to losing color.
For gold vermeil, which is gold plated over sterling silver, tarnish will happen but as the base metal is sterling silver, it'll become a sterling silver piece once you clean the tarnishing part.
The speed at which this color fades will depend on various factors, such as the use of chemical products on the skin, how much the wearer sweats, or even the pH level of the individual’s skin.
For this reason, it is particularly important to ensure suitable care of your gold vermeil jewelry.
Keep in mind that only real gold jewelry ( not gold-plated, nor gold-filled ) won't tarnish and will last forever.