There are a few aspects that need to be addressed.
1) Diet & Oral habits: Often, drinks with natural or artificial coloring will stain the surface of the enamel and any tartar (calcified plaque) that rests on your tooth. Some oral products (ex: smoking) and medication (ex: some mouthrinces and some antibiotics) are also known to cause discoloration. ...
There is no healthy way. Whitening/bleaching do not change the shape of your teeth but alas, dentine doe not bleach well, if at all (it just gets more sensitive to temperature change). Veneers done well will have a 'good' shape to ensure gum health. As for trying to find something to paint on, let's explore that if you place a opaque white dental liquid ...
Hydrogen peroxide is an oxidizing bleach. It reacts chemically with the types of molecules that contribute to color.
So, it doesn't really remove stains, nor does it coat anything, but it does make colorful things not-as-colorful, just like if you wash your white socks with chlorine bleach.
I have not found any whitening properties of tea tree oil but it can help prevent tooth discolouration and I have seen toothpaste with tea tree oil sold in shops.
Jain et al. (2014) states:
Tea tree oil’s major active component is terpinen-4-ol (30%–40%). This compound is responsible for its antibacterial and antifungal
properties [(Arweiler, et al. 2000)].
Being an very mild abrasive charcoal is indeed used since ancient times to clean teeth. This behaviour is seen among the natives of Africa and Digitalia even now.
Examples for recent use in Africa: Oral health related behaviors among adult Tanzanians: a national pathfinder survey.
Oral health practices among pregnant women in North Eastern Nigeria.