 
Are your teeth not as pearly white as John Stamos's or Beyonce's? Are slightly yellow teeth healthy? Have no fear! If your teeth are just a bit off white with a little bit of yellow, they are likely still healthy!
Your tooth has white enamel as an outer layer, but just underneath is your dentin, which is a yellow hue. And since everyone's teeth are a little different, sometimes the translucent enamel is thinner, leading to a more yellow-ish appearance. Enamel thins naturally as we get older, so it's normal for teeth to darken or become more yellow over time.
Intrinsic staining
Intrinsic stains can come from many sources, including medications like antibiotics or prescription mouthwashes, certain genetic conditions, trauma, or fluorosis. 
Extrinsic staining
Extrinsic staining happens over time and is caused by environmental factors typically related to diet, oral hygiene habits, or bad habits like smoking and drinking.
Foods that stain teeth
For most people, the yellowing process is accelerated by the things we eat and drink and other external factors. These include:
Berries: Although the antioxidants in berries provide health benefits, their deep hue can cause staining (think about cherry juice on your favorite shirt!)
Sauces: Brightly-colored sauces like curries and tomato sauce can also contribute to staining, and the acidity of tomatoes makes them stain more! 
Coffee: The dark color and acidity of coffee both have a detrimental effect on your teeth.
Tea: Black tea, in particular, can be more damaging than coffee. Even lighter herbal teas can erode enamel and cause staining.
Wine: The tannins in red wine are responsible for turning teeth into a shade of grey. White wine, meanwhile, although not directly responsible for staining, can make existing stains darker.
Sugary drinks: It's well known that sugary soft drinks cause tooth decay, but because they do this by wearing away that bright tooth enamel, your teeth will appear darker over time, too. 
Smoking: The nicotine and tar in tobacco can stain teeth very quickly. Over the years, heavy smokers may find their teeth turning brown, known as smokers' teeth.
Some Antibiotics: Tetracycline can cause staining from taking this antibiotic as a child. 
yellow teeth culprits. 
How to Minimize Staining
Try having the (above) foods alongside foods that can prevent tooth staining, such as cheese, lettuce, celery, carrots, apples, and cauliflower. These either help clean teeth through a gentle "scrubbing action" or work to neutralize the acid that damages enamel.
And to maximize the strength of your teeth by remineralizing that enamel, make sure to allow that fluoride toothpaste to stay on your teeth after brushing! No rinsing!
WHY Don't teeth stay white?
For most people, teeth stains are caused by a lifetime of consuming stain-prone food and drinks like coffee and tea. In addition, other stain-causing habits like smoking and chewing tobacco are also common culprits.
For others, it’s not a matter of bad habits but a combination of age and genetics, or medications that causes white spots on teeth. Teeth whitening treatments can help brighten your smile by several shades. However, going back to these stain-causing habits could affect how long your results last.
Here at Harte Dental, we really just want our patients to have healthy, pain-free teeth and jaws, but if you'd like to brighten up those teeth to look like a Greater Boston celebrity, (a Miltonite Brad Pitt or Zendaya) call us and schedule an in-office whitening! In and out in about an hour and you're ready to show off that smile at that wedding, beach, hiking hot spot, or wherever summer takes you!
Call us at (617) 696- 5257 or email us at ContactUs@hartedental.com. Come see why we've been voted Best Dentist in Milton, Favorite Dentist in Milton, and are 5 star Google reviewed with over 630 5-star Google Reviews!
Info from https://www.pronamel.us/amp/are-yellow-teeth-healthy.html