Fyi most 18kt watches have a alloy content to it which brings the color of (23.99kt ) yellow gold to white gold, some times our bodies creates some toxics which reacts to the alloy and long term the color of the metal changes.
What is really required is for a professional watch maker to get you a approximately 5 to 10 microns of Rhodium to the watch which should last you for a good time,
I always use a micro fiber cloth to clean and maintain my watches, I manage a jewelry store and a watch store here in the U S Virgin islands and I'm well aware of your situation it took me almost a few years to figure this out. hope this works for you .
If you are still hesitant call the guys at Rolex can take care of this for you.
Take care,