Why are some people's teeth yellow?
There are many factors affecting the color of your teeth. One of the most important factors affecting the color of your teeth is actually your genes. If your mother and father have naturally yellow teeth, then chances are that you will have a similar teeth color.
Another thing that affects the shade of your teeth is what you eat and what you drink. Certain foods will stain your teeth if you consume them on a regular basis. Example of such foods are berries. But the foods are not the only reason for tooth staining. Two very popular beverages will badly stain your teeth if you drink them frequently. The first one is coffee and the second one is a red wine. Smoking will also affect negatively your teeth appearance. Some antibiotics like Tetracycline can also stain your teeth.
In conclusion you cannot affect the natural color of your teeth, but you can avoid foods and beverages that stain your teeth.