Flossing indirectly makes your teeth white. Flossing allows for you to reach bacteria that is stuck in between your teeth, causing your teeth to be more healthy. Healthy teeth are white teeth! In order to make your teeth white, also try whitening mouthrise.
Thick white enamel makes natural white teeth. Enamel can be stained over the years (smoking, tea, coffee, red wine, etc.) or can become thinner by consumption of acidic foods (soft drinks, ice tea, red bull, orange juice). An artificila way of making white teeth is dental crowns of dental veneers.
Healthy teeth should NOT be brittle. Instead, they should have healthy enamel. A thick enamel makes teeth strong and bright white. Teeth without enough enamel look off-white or gray, and can become brittle. This lack of enough enamel can lead to tooth weakness, cracking, and breakage.