Must be genetics. None of us have white teeth, all cream. Mine are darker cream, but not dirty. I remember my baby teeth, they were white, then when they fell out, new teeth came through, they weren't white. I've drunk milk all my life, brushed them, flossed, still they aren't white. I don't smile. My sister had a bridge done (think that's what it was called) when she was 16 (now 56 almost) that's creamy white. I think WHITE, think fake.
On the other hand, my gran, who died in 1983, had her own white teeth, dark brown/black hair with a few streaks of grey and cleaned them with a dark red toothpaste. After she died, I remember seeing Betty Turpin/Betty Driver on tv and thinking, wow, looks just like my gran. My grandad had a full set of false teeth.
Both my parents have crap teeth, us girls didn't stand a chance!