Why your teeth are the color they are
Yellow, brown or gray — and why each responds differently. The color you see is dentin showing through enamel.
Nobody has white teeth. Not naturally. The color you see is yellow dentin showing through a semi-translucent layer of enamel — and that's exactly why whitening works on some people and does nothing for others.
Two layers
Enamel on the outside is thin and slightly see-through. Dentin underneath is naturally yellow. Thin enamel means more yellow shows, and enamel thins with age, acid and scrubbing — which is why teeth yellow even when you brush perfectly.
Two kinds of stain
Extrinsic stain sits on the surface: coffee, tea, red wine, tobacco, plaque. A cleaning removes it; gel barely has to. Intrinsic color lives inside the tooth: age, genetics, old trauma, antibiotics as a kid, too much fluoride growing up. That's what peroxide is for — and what it can't always fix.
Three base tones
Yellow is the easy one; peroxide loves it. Brown is mixed — often surface stain or fluorosis, and it depends which. Gray is the hard one: usually intrinsic, tetracycline, old trauma, a dead nerve. Peroxide does the least here.
Do this now
Go to a window. Pull your lip back. Yellow, brown or gray? Any patches or bands? One tooth darker than its neighbors? Write it down — it's the first thing the team will ask.