>Do they have a name, like "Russet" or "Idaho Baking Potato" or something
>that I can ask my grocer about?


Elaine,

I'm far from a potato expert, but I've only seen them sold as purple
potatoes, never an exact variety. So the produce guy should know just
by "purple potato". I don't know if there is only one variety or just
like everything else, the stores have dropped the variety names. (You
use to buy Haas or Bacon or Fuerte avocadoes, now they're just labeled
an avocado with no variety. Same with peaches, plums, you name it, and
maybe even potatoes.)

Wish I could be more help,

Ken