The dough will be even better if you use 100 g of shiratamako + 20 g of joshinko. The resulting dumplings will be chewier and fluffier than just with shiratamako.
Use silken tofu for best result. You want to mix the flour and tofu in a 1:1 ratio until the resulting dough is firm as your earlobe.
Knead the shiratamako and tofu. Divide it into thirds and colour 1 part pink using the red colour, and 1 part green with the matcha. Leave the last portion white. Form the dough into balls.
The dough should be firm as your earlobe. Form the dough into small balls. Don't worry if the dough is a little stiff, just make the dumplings and immerse in boiling water until 2 minutes after they float to the surface.
Boil the dumplings, cool, then drain. Skewer the dango and serve.