…is Regenbogenschüsselchen. It means ‘rainbow cups,’ and refers to concave electrum coins minted by the Celts. That explains the ‘cup’ part; ‘rainbow’ is because they were often found after heavy rainfall in plowed fields, that is, they appeared to be the pot of gold (alloy) that appears at the end of a rainbow.
I wonder if this contributed to the various myths about leprechauns. After all, ‘Rainbow Cups’ (like Lucky Charms) sounds like a disgusting breakfast cereal marketed towards children.