A.,
I have been in the jewelry business for several years. I was reading the reponses you recv'd.
Let me start by saying white gold needs extra care! Do not use a harsh chemical such as amonia, peroxide, window cleaner etc...and do not use toothpaste it is much to abrasive for white gold. Using toothpaste is an old wives tale from WAY BACK. I am always amazed at how many people bring their rings in to me with toothpaste stuck underneath the diamond and in all the little nook and crannies. I get the same stories everytime!
White gold is not a pure white metal such as platinum or silver. It is made from yellow gold and therefore has a slight yellowish tint to it. To make it pretty and white it is dipped into rhodium plating. This will rub off with everyday use. Lotion, hair products, grabbing the steering wheel, clasping onto misc items throughout your day,etc... everything you do will wear off the plating. You WILL start to see a difference in color, starting usually on the bottom.
The best way to keep it clean and shiny at home is a very soft bristle toothbrush (to get to the nooks and crannies)and hot water. Be sure to keep up on your regular maintence with your local jeweler at least every 6 months. They should check it throughly in front of you for any loose stones (especially before they drop it into an ultrasonic machine)and check the thickness of the prongs holding your diamond. Most jewelers offer this service at no charge
As far as the rhodium plating, your local jeweler can re-dip for you
Another Tip...don't wear your rings at home...I know you never want to take it off but, you can make less trips to your jeweler and save $$$ for repairs. My jewelery is the last thing I put on when I get ready to leave the house and the first thing I take off when I get home. It saves SO much wear and tear on what you hold dear.
Save your $$$ and take good care of your ring