At the verdulería (veggie store):
Day 1
Me: What potatoes are better to make gnocchi?
Seller: Black potatoes - here you are!
Me: Great, thanks!
Day 10:
Me: I need black potatoes to make gnocchi!
Seller: I have white potatoes, they are just washed black potatoes. They are the same thing, really!
Me: Great, thanks!