This is something that is quite often misunderstood.
Nearly every mass manufactured piece of jewellery in white gold is given a Rhodium plating at the end of its being made. Rhodium is a metal in the Platinum family of metals along with Platinum and Palladium. It is very bright and white, similar to Platinum, and has a very attractive appearance.
With normal wear and abrasion and friction from clothes and everything else that normal life entails, this plating wears off. It is a few microns thick and sits on the surface of the metal. If the ring underneath is made of white gold, the this is the metal that you begin to see showing through.
There is no cause to be alarmed. You can get rings re-plated if you wish to return them to their original appearance.
But we feel this is a shame, and maybe a bit uneccessary.
White gold is a beautiful and interesting metal in its own right. 18kt white gold is 75% pure gold (ie; yellow) and 25% remaining alloy which can be a mixture of silver and palladium to draw the colour towards white. This white colour is always going to be a tiny shade darker and have more 'warmth' in it than the same ring in Platinum. If you see a naturally finished white gold ring alongside a silver ring and a platinum ring, they are all white. And they are each different shades of white with their own character.
If we are making a wedding band to sit alongside a pre-existing engagement ring which has been plated then we will plate the band so that the rings match eachother. Or if it is the informed preference of the wearer that this is the finish they want then we are happy to oblige.
As a rule though we prefer to finish our metals to their natural appearance and make the best use of their unique attributes.