My Veneers Look Yellow, What Do I Use to Whiten Them?

There is nothing that can be done to improve the color of the veneers, short of cutting them off and replacing them.

If you think that the color of your veneers have yellowed over time, its possible that they are made of a plastic composite material. Normally, quality porcelain veneers will not change colors and can't be whitened.  
When choosing a shade for your new veneers, always error on the side of the whiter shade when choosing between two colors. Also, it's important to make sure you are happy with the color before having your new veneers permanently bonded on to your teeth.   

There are two type of Veneers...composite and procelain.  If you had your veneers made in one appointment in the dental office, they are probably of white material or resin. This is called a composite veneer. Your dentist can polish the composite veneer and remove most of the stains.  If your veneers were made of procelain and, most are porcelain, there is no way to take the yellow color out of the porcelain. You will have to have them removed and replaced with new ones.