what's the deal with yellow teeth?

[christine breen]

No: HPFGUIDX 31125

Why did Rowling go out of her way to mention that both Snape and Karkaroff
have yellow teeth?  Do yellow teeth seem more menacing?  I know coffe and
smoking can stain teeth, so I'm going to assume something about being a
death eater has stained their teeth yellow.  Drinking potions?  Do
polyjuice potions stain teeth?  Are we to assume that since yellow teeth
was mentioned with Snape and Karkaroff, and they were both DEs, that
anyone with yellow teeth is/was a DE?  Maybe it's a time delayed
curst--when someone leaves Voldemort and ceases to be a DE their teeth
turn yellow?  Who knows.
Christine