I can see yellow on my white veneers, bleaching does not effect them at all. Could it be polished off by a dentist?

Typically, veneers themselves don't pick up stain since they are not porous. One question I have is was the yellow on the veneers initially? Sometimes that yellow stain is intentionally placed on the veneer to give a more natural look to the veneer. Depending on how that stain was applied, it could be polished away. If this is something new, there are polishing devices that we use that could remove this yellow discoloration. It's important to keep the veneers nicely polished to keep plaque away from them.