This isn't made with green potatoes, but is rather made green by the addition of peas and lettuce.
HEAT OIL IN 3-QUART SAUCEPAN over medium-high heat. When hot, add onion. Cook until softened, about 4 minutes, stirring often. Add all potatoes and cook 1 minute, stirring constantly. Add 4 cups stock or broth, dillweed and cayenne. Bring to boil. Simmer, covered, 20 minutes. Add peas and lettuce. Cook until potatoes and peas are completely tender, about 5 minutes. Puree soup in food processor with metal blade until smooth, about 2 minutes. Return to pan. Thin as desired with remaining stock or broth. Adjust seasoning. It's bright green when freshly made; the color lightens on storage but it's still appealing. Can be made 3 days ahead and refrigerated. Can also be frozen as long as 3 months. Serve hot or chilled. Makes 6 1/2 Cups