Add spinach leaves and ½ cup water to a food processor or blender and puree. Remove from the processor and add water until you have a thin liquid.
In a large bowl, add flour and salt for the white dough. Add ¼ cup lukewarm water while stirring the flour with a rubber cake spatula or chopsticks. Knead by hand a couple times, gathering up the dough into a ball. It should be relatively dry and non-sticky. If you find the dough is too dry, wet your palm with water then tap the water on the dough to continue kneading; do not add water directly to the dough as you might end up adding too much water. If you find the dough too wet, add one teaspoon of flour to the dough and continue kneading, adding another teaspoon if needed. Let the dough rest about 10 minutes. Then return and knead the dough gently until it is smooth and elastic. This will take 2 to 5 minutes (depending on the flour and temperature). Cover with a thin damp towel.
Repeat the process for the green dough, using spinach juice as the liquid.
Both doughs should then rest for 30 to 60 minutes. The longer you wait, the softer it will get, but if you wait too little time, you will have difficulty rolling out the wrapper. If the dough becomes too soft after a long period of resting, gently knead for about 30 seconds. If the dough resists being rolled out, let it rest for a bit longer. Poke a hole with your finger on the dough, and if the dough doesn't bounce back, it is ready.
Lightly flour your work surface. Roll both doughs into a long log about 1 inch thick in diameter. Using a rolling pin, roll the green dough out into a long, oval shape. The length should be as long as the white log, and the width should be enough to wrap around the white log. Place the white log on top of the green log, spread a small amount of water with your fingers on the top, then wrap it tightly. Roll the log a few times to ensure the two colors are sticking together.
Cut the log into 30 portions of similar weight, about ½ ounce (13g - 15g). Work with one piece at a time, keeping the others under a damp cloth. Press flat with your palm to form a round disk. Use a rolling pin to roll into a rounded wrapper 3 to 4 inches in diameter. Dust corn starch on both sides (or flour if it is on the soft side) and set aside, covered with a damp cloth.